Like the versatility of the P320, but the PDP fits like a glove. Haven't felt a grip this nicely.
Just watched the Honest Cowboy review for the PDP and surprised to hear the PDP is a bit snappy.

Between these two, which do you prefer and why?

Unwanted discharge issue for the 320 isn't encouraging. It's happened too many times to be a rare freak thing and should be addressed. To be fair, there are massive numbers of them circulating, so such trends will be more visible.

The PDP is no snapper than the PPQ. Slightly snappier than the main rivals with +P ammo, but no big deal for grown Men, honestly. PDP has one of the best triggers in the business and point and shoot is excellent. I'd go for the PDP Pro 4.6".

I never thought anything would pry my PPQ out of my hands esp. after it served me well at multiple Gunsite and other classes, but I picked up a Gen 1 PDP Compact used for nearly nothing.

The PPQ hasn't left the safe since. I guess it worked out and can keep the p320 company in there.

For me the PDP is what I imagine Glocka are to some folks.

Bonus that all the mags carried over from the PPQ to the PDP.

Some of the best advice I’ve seen in this forum in a while.

I've had a couple of P320s.  And one PDP-F.

I still have the PDP-F.  Fit and finish and trigger is better for me.

I've never even shot the PDP and I'd choose it over the 320.

I have both , a real Sig M18 and a new PDP Compact , they are head and head they feel great in the hand shoot great , mags a about the same . PSP just went with the Walther PDP !I talked to a few that got there s and they like it , they just went from the Sig 227 in 45 cal they been using for 10 or more years .

I have both , a real Sig M18 and a new PDP Compact , they are head and head they feel great in the hand shoot great , mags a about the same . PSP just went with the Walther PDP !I talked to a few that got there s and they like it , they just went from the Sig 227 in 45 cal they been using for 10 or more years .

See if your local range has them both to rent, shoot them both and see which one you shoot the best with. Ignore all the stupid brand tribalism that seems to be so prevalent with pistols now days. Both options you are looking at are great, you really can’t go wrong with either. For me, the P320 shot better and it also had the added benefit of being modular so I could custom tailor the pistol to fit my exact needs and wants. The PDP though is an excellent pistol with a really great trigger out of the box. PMM makes a great comp for it that really makes it a flat shooting and fast pistol. You really can’t go wrong with either choice.

This.^

The 320s I've shot were garbage. Shit triggers, lackluster accuracy, and one can definitely feel the cheap frame flexing, which isn't an issue I've ever come across on a polymer-framed pistol. Also, SIG USA:

I own several P320s and so I can confidently say you’re FOS. The triggers out of the box are better than most, not the best but shit? No. Accuracy is excellent and that is to say it is in line with similar pistols in the polymer striker fired market. All polymer frames flex under recoil. Watch any poly framed pistol firing in slow mo and you will see the dust covers flexing. The good news is if this bothers you, you can easily replace or upgrade your module to whatever you like and that includes changing it out for aluminum and there is even a steel frame coming out for the P320. I realize it’s hip to rag on Sig for the long since addressed P320 drop firing issue or the cops who claim their gun just went off despite nobody ever being able to replicate the supposed failures and Sig winning law suit after law suit, but let’s keep the claims in the realm of reality and not dumb shit you read on the internet. Before you default to calling me a fan boy, I own pistols from just about every major manufacture and shoot a couple thousand rounds a month, I like all of them pretty much, they all have pros and cons but Glocks, Sigs, S&W, H&K, Beretta, Walther, there are really no bad options when it comes to polymer framed striker fired pistols now days. Buy them all if you can. If you can’t find the one that works best for you and train with it. Being a fanboy is stupid.

I have shot both and own a P320 but do not take that as endorsement for the P320.  Both are outstanding pistols and both have their quirks and nuisances plus benefits/cons.  I would probably own a Walther PPQ/PDP if adopting another magazine into my already crowded color pallet of magazines would not cost so much.  
There are things I do not like and like about the P320 and things I do not like and like about the PDP but let us get real for a moment.  The things I do not like about pistols usually amount to minor quirks that I have to pick out to be objective that I am really analyzing a pistol.  Anyone who owns a brand X and says they are the best pistol ever made with no flaws or they are absolutely perfection is brand bias or a fanboy.  The same goes for any other pistol on the market you have people who are incredibly bias or straight up fanboys that cannot fathom liking another pistol or it is complete blasphemy to like brand X.  Also you have the group that seek validation that they made the right decision by choosing brand X and to praise brand Y would cast doubt on their choice of brand X.
When you make blanket statement that something is garbage, has shit triggers, lackluster accuracy, or that you can feel frame flexing you are exposing yourself as one of the types I mentioned above.  If what you said was the case and your statement had merit you would not have so many people buying and shooting P320's the pistol would have completely flopped.  Example the Remington RP45 it was a complete piece of trash and it flopped so if the P320 was as you say it would have flopped also.  So we know pistols can flop because they are bad designs or just terrible execution.  Sit back relax and maybe give alternative pistols on the market a shot because there are some really nice and fun pistols out there that people just ignore because they get so caught up in only liking what they like and cannot stand that others like something else or did not make the same choice as you.

Well stated.

If there was any fault with the P320 platform, I would not own 18 of them. These new Walthers do not impress me much. In addition, I have owned many firearms over the last few decades by many different manufacturers, so I am not so much a fanboy, but I try to stick with those I know that work and work well.

I've shot both, alot.

PDP - there is absolutely no comparison - even more so now since Walther updated the slide and the PDP no longer will get the fake dead trigger problem the internet freaked out over.

Not picking on you, but as a guy who got issued the M18 before I got out, it's hard not to giggle at that last line.  My ATL got smacked in the face by his rear sight and optics plate within the first few strings of fire.  Picking through the gravel on the flat bay for that stupid shit may have tainted my first experience taking the M18's out after they replaced the CQBP for us.  

The issue of sights disconnecting from the slide is hardly exclusive to any brand.  I have seen two MOS Glocks leave slides before and seen my fair share of screws give way on multiple brands of pistols and sights.  You should have seen the look on my friend's(a guy who does not like scratches or dings on anything) face when his brand new RMR went tumbling across concrete.  We had finished shooting for the day and he let the slide go on empty and when the slide stopped Newton's first law took over.  I had thought he threw something at me as a joke but it was his sight going airborne right in front of me plate and all.  I thought it was going to cry for a moment.

I have a PDP Compact and a Sig P320 Pro Carry with Med and Small grip modules. Both are great, accurate and completely reliable.

P320 is a little more concealable (my opinion), I like the X-Carry type grips on mine over the standard baseball feeling grips. Wilson grips look great too, but I haven't held them.
17 round mags are nice (and I have some 21 rounders), grips a bit longer than the PDP Compact, because... compact. Sights are better on the P320 out of the box on mine at least, the Xrays.
Trigger is good. Never any issues.

PDP; aggressive texture, great trigger. Might have a bit more felt recoil out of the box, but that's due to an 18-19 lb recoil spring. I dropped in a 15 lb with steel recoil rod and it shoots like a dream.
I wish Walther used the removable fire control module like Sig, because it'd be nice to be able to use an F style grip mod. But the standard compact still fits like a glove.
15 round mag limit unless you can find a 17 round deal, from a PPQ (maybe?). Seems like they should have the 18 round mags with some sort of baseplate to fit. Or just buy the full sized frame version.
Also never any issues.

My goal is to just keep one platform to standardize mags and holsters, etc. I may sell the P320 if someone talks me out of it. But some days I like it better so still deciding.
Then I impulse bought a PSA Micro Dagger and I can't explain why. Now I "need" a Shadow systems 920 something-or-other. I have issues.

Personally I think the design of the M17/M18 rear sight assembly is not that great but pistols without sights milled directly out of the slide are at risk of leaving the pistol. I’ve seen Glocks, HKs, P226s and P229s as well as the newer Vertec slide berettas lose sights. This has become an even bigger problem with the addition to optic plates. Now those are starting to fly off along with optics. It is the nature of the beast. You have reciprocating mass with an object attached to it. Failure is inevitable. That kind of failure you described is not one I would hold against any brand.

You know, I had a Walther PPQ in .45 acp.  Very nice shooter with a great trigger, but I got rid of it.  Just looked too much like a High Point.

I've also gone through a few P320s and still have two.

First is a P320 M17.  With it I have 4 upper assemblies.  
- The original M17 FS 9mm upper.
- A 3.9" X5 compact 9mm upper with a Delta Point Pro on it.
- A .40 S&W full size upper.
- A .40 S&W 3.9" compact upper.

My other P320 started as a FS .45 acp.  It has:
- The original 4.7" FS .45 upper.
- A 3.9" stainless compact .45 upper.
- An X10 5" FS 10mm upper.

Not to mention if you don't like the grip you can change it.  I stuck the .45 FCU in an X10 grip module because I like the way it feels in the hand.  I may get an X5 grip module for the M17.

I have a lot of options with these two guns.

As far as the unintended discharge thing, just not something I'm worried about.  I don't think I've heard of any military or civilian users having the problem.  Just seems to be cops.

I was a cop for 25 years.  I can tell you it's not difficult to get something in your holster while re-holstering.  Duty jacket tabs, draw strings, loose clothing, etc.  Done it myself.  Not hard to imagine something getting caught up in the trigger.

I really like the versatility of the P320 series and would pick it over the Walther.

Consider the GGP slide, at least for 9mm anyway. You can mount your MRD and still have your iron sights as you want them. I never liked SIGs "X" pattern MRD mounting anyway.

I'd take a Walther over a Sig P320 any day of the week.  Owned an M18 and didn't care for it, I liked my PPQ M2 much better.  That said I do love the P226 and P220 series guns.

Pdp

Then your CATM section didn’t do what the DoD directed and apply thread locker and torque to value.

The rear sight issue is a well documented problem not because it’s faulty but because Sig failed to torque them properly before shipping. I haven’t seen an M18 yet that failed due to engineering flaws and I’ve seen a lot of them.

I was in a similar situation. But mine was between the PDP and the Echelon. I went with the Echelon and couldn’t be happier. The PDP is a good gun but she is on the chunky side.

After shooting both, I would say the P320 is a better performer on the clock. The PDP has better build quality and a better trigger, but does have a touch more recoil. Not that it's unmanageable by any means. I guess it depends on what factors you care more about.

That seems to be what I an reading and hearing in videos.

Hit the indoor range this weekend and was going to rent one, but there was a 30 minute wait.
Think I may just shelve the idea of the PDP and stick with my current P320 for now.

I have multiple 320s and PDPs and like both a lot. I have put thousands of rounds thru both. I put AXG frames and Lok grips on the 320s and love them. My PDPs are stock. Overall, the Sig triggers are a bit better, but the PDP triggers are very good. You can’t go wrong with either pistol.

I was an early P320 adopter.  The novelty of the design totally appealed to me .  I bought the first P320 carry I could find.  No matter how much I shot it, I just didn't love it.  It just didn't stand out from anything I already owned in terms of performance.  It was accurate but not particularly flat shooting.  It was probably the least appealing gun I owned.  I completely lost interest in it and sold it off.  It's not a bad pistol but to be there is nothing about it's performance that makes it stand out.  I've since shot some P320's that have been tuned and customized and none have made me feel ike I needed to own one again.

This Memorial Day break I got to shoot my P320 with my friends PDP.  So I actually got to do a little side by side comparison but not a true apples to apples comparison.  My P320 is comp-ed and his PDP is not so the recoil and muzzle flip between the two are not easily compared.  One thing I will note when comparing the PDP to one of my Glocks it definitely has a more felt impulse in the cycling.  My split times were higher with the PDP than when compared to my P320 and just slightly higher than with my Glock 17.  This could be because I am more adapted or shoot the pistols more but the P320 was the clear winner because it is comp-ed.  The trigger while it is a little better on the PDP to me all three of the pistols have good triggers and while firing it is inconsequential and really only notice the feel when dry firing.  Comparing my P320 and the PDP the difference was marginal and I have a stock P320 internals and skeleton Sig trigger.  I will say the PDP feels better while dry firing but the P320 trigger is not exciting to dry fire but no P320 is exciting to dry fire it is probably the weirdest and most boring trigger feel of any striker fired pistol.  Dry fire trigger feel really means squat they both have outstanding trigger while firing live ammo.  Personally the P320 trigger feels better while firing than the Glock or PDP but that could be because I am accustomed to it and can predict it just like my Glock.
One thing that even since the PPQ that has been a complaint of some is the way the slide feels while reciprocating on the Walther pistols it really does make the 9mm pistol feel closer to a 40SW.  Maybe a Walther with some slide lightening would feel better but that is something that stood out when I was really focused on all the nuances.  
Other pistols that were present I shot my CZ P-09, HK P-30, CZ SP-01, Sig P226, P365 Macro/XL, Glock 19, 1911's, 2011, P10c, and several more Glocks.  To keep this more on target I only included the Glock 17 since it seems to be kind of a baseline in striker fired pistol neither being the best of the best or worst kind of something many people are familiar with.

Awesome reply and summaries a lot that I have been reading.
I am saving my money use it toward other firearm related products.
We can officially close this thread.

https://www.psmagazine.army.mil/News/Article/3245225/m17m18-mhs-rear-sight-inspection-and-repair/
https://www.psmagazine.army.mil/News/Article/3245225/m17m18-mhs-rear-sight-inspection-and-repair/

I think the design could be better. The single screw holding everything together allows for a total failure. Strangely the civilian M17 and M18 have a better designed rear sight using two screws but it requires further disassembly of the slide to remove the optic plate.

I have a PDP compact that I got right after they first came out.
I upgraded to their dynamic trigger and eventually added a threaded barrel and a comp.

The stock trigger was really good, the dynamic is a bit better.
Even with a comp, it's still snappy. If I had it to do over, I probably wouldn't bother.
(had to go to a lighter recoil spring)
I probably have 5K rounds thru it and the only issue I ever had was after adding the comp, but it's been fine after changing the recoil spring.

Maybe the full size is less snappy? Who knows? I'd love to try a steel frame, but I don't plan on buying one.

I originally got it because I wanted to try shooting a local IDPA match.
After a couple of years, I changed to a Shadow 2.

I've never shot a P320, but the grip felt uncomfortable to me, so I have no input on the 'vs'.
Just thought I'd give some PDP insight.
For my uses, I'd say neither. Too big for concealed carry (for me) and not as fun to shoot as the Shadow 2.

Whatever you decide, I hope you really enjoy it.