I have both a Mossberg 835 and a Benelli Nova H20, Supernova H20 and Supernova Tactical.
To my mind, the Nova/Supernova is the best pump shotgun currently availible. Its "bomb-proofness" is second to none. It has a chrome lined barrel, steel receiver with a polymer overlay and other features that enhance and improve durability/reliability.
I purchased my 835 right when 3.5 inch 12 gauges started to become popular. It was my dedicated goose and sometimes turkey gun. I have always prefered Franchi and Berettas for field guns but I needed a 3.5 inch shotgun but hunting Benelli's aren't all that appealing to me... I have put it through alot of abuse and while its still alive and kicking, its failed me numerous times.
The safety has broken more times than I can remember. It constantly freezes and any type of forceful manipulation will shatter it, which renders your gun useless. The magazine springs in Mossbergs are generally junk. The trigger guard has also been broken several times. The action froze once and the action bars got bent. This is only what I can remember...
I had a Nova when they first came out around 2000 or 2001 and put it through the same abuse before selling it. The Nova had WAY more recoil without the porting and mercury reducer, but it was a much more robust, durable, reliable and problem free gun.
I have since converted my 835 into a defensive gun with a shorter barrel and mag extension. I would trade it for another Supernova or Nova in a heartbeat.
The Nova is a much better gun.
ETA: I have hunted turkey and other birds with a red-dot and I am pretty sold on it. I have a Burris Speedbead on my Supernova H20 and Beretta Pintail. Any advantage a RDS offers when shooting people is relevant when shooting moving animals. A Burris RDS with multiple, color/pattern changing reticles would be awesome on a turkey gun. I use both an EoTech, Zeiss Zpoint and Micro Aimpoint on shotguns.
Before I drilled and tapped a gun, I'd probably look at getting one of those B West mounts.