Well, I recently purchased a Benelli M1S90 Tactical and I've put over 400 rounds through it without a malfunction, cleaning after the first 300 rounds. I have a buddy who owns a M3S90, and he has had excellent luck with his as well, nary a hiccup in several thousand rounds, all of which in semi-auto.
The M3 can use a folding stock, while the M1 cannot because of the recoil spring tube in the buttstock.
The pump feature is neat if you want to play around with "less lethal" rounds like the rubber buckshot or slugs, or tear gas rounds. Otherwise, it should cycle even the lighter birdshot loads after a break in period of about 500 rounds (this is as per the Benelli sales rep).
Only negative thing I think about the M3 versus the M1 is that the M3 barrels do not come with choke tubes. The M1S90 Tacticals now come with the 3 basic tubes, F,M, IC. The M3 barrels are IC, which realistically will do most anything you need to do with a combat shotgun.
Buy the Benelli, you won't be sorry. It's amazing how damn simple the mechanism is.