I know the standard SKS is best in stock configuration and fixed 10rd mag. I have those covered. Over the years I have picked up an SKS here and there whenever I found one at a good price and have some mixmasters and bubba specials. I would like to stock up on some higher capacity detachable mags if I can find some that work well.

Tapco 20rd mags had a good reputation but they are out of business now and not available. Seems like ProMag is my best option currently available and about the only one that I'm finding. Midway has them on sale right now but I don't want a bunch of them if they are complete junk.

Is there a better 20-30rd option than ProMag?

Not what you are looking for but you could also look for some of the fixed 20 round Chineese “star”’magazines.

The only detachable SKS mags that I had any luck with was the Tapco 20 rounders, I still have a few even though I converted all my SKS back to fixed mags.

I’m not talking detachable mags.  There was a fixed 20 round available and while I don’t have any actual experience with it, I have heard they are reliable.

It does look a little goofy mounted on the rifle imho.

I’m a purist when it comes to the SKS, so this is not my 1st hand knowledge.
I hear the Tapco mags are very good. I’ve also read that the god awful looking mags made in Detroit years ago work great. They’re the 30rd ones that look like they were made in a high school shop class.

Don't leave Tapco mag loaded in storage.
The lips will relax, and the mags will unload themselves
Had a bunch of them stored loaded, and one day I opened my closet, and there was ammo all over the floor.

They are OK kept loaded in the rifle, with the bolt closed, as it keeps the rounds from putting pressure on thew lips.

I used to have one of those Star 20 fixed mags like 15 years ago, I sold it locally to a guy because he offered me like 80.00 for it alone in a sale along with some other SKS parts. It shot and cycled fine but loading with stripper clips was a bit janky, wished I kept it because they go for crazy money now. I probably would have kept it if I had a Chinese SKS but at the time it was in a Yugo M59 and I decided to put the matching numbered factory fixed 10 rnd back in.

i put a Chinese star fixed 20 on my first SKS back in the 90's, ran great, as good as the factory 10. Those are too pricey these days. The cheap copies are junk.
Last one I bought had a Tapco 20, and the lips were bent cause the last owner pulled em out on a closed bolt. A new Tapco ran just fine but even with modding didn't load as easy with strippers vs the fixed 10.
I think any removeable mag is gonna have the issue of not being removeable on a closed bolt. That's a PITA. And removing or loading the mag takes two hands, one to pull the release tab, one to remove the mag.
Never tried one but the Archangel mag at least has a built in release lever so it CAN be removed one handed.

I have that 20 on my norinco, runs pretty good, but not as good as the stock 10rnd, I have two duck bill 30's ones used, and didn't run right when new, the other is still unused,