Several years ago I was in the market for a semi-auto water fowling gun. I had used a Rem 870 for 20 years to hunt ducks, but decided it was time to try semi-auto. I went to the gun shop and narrowed my selection down to the two guns that fit me best. Shotgun fit should be your number one priority. I had decided on the Benelli SBE or the Winchester Super X2. I read numerous reviews and talked with fellow hunters about both guns.
I ended up going with the SBE because of the ease of cleaning and the adjustable stock shims. To clean an SBE you would remove the magazine nut as normal, however the entire receiver breaks down. This makes it very easy to clean the gun at the bench or in the field. The parts are very simple on the SBE. The adjustable stock shims allow the shooter to adjust the guns drop on the stock to be fit to the shooter. This is helpful if you will be using the gun to hunt waterfowl with heavy jacket on and also dove hunting with just a t-shirt ( may affect how the gun fits some people). I had heard many stories about how reliable the SBE was so I decided to perform a little test. I hunted all of December and January and never cleaned the gun, hunting roughly 3 days a week in salt water and mud. I had no problems at all with the gun. The only negatives I can see with the SBE are, Price and Benelli states that the SBE will not shoot 1 1/8 ounce loads or lighter. I must have gotten lucky because mine would shoot 1 ounce loads right off the shelf. I know several others that have older SBE's that once they were broken in would shoot lighter loads. For shooting waterfowl I recommend IC choke with Winchester Supreme 3 inch, #2 steel. You got to let the birds work the decoys, let them get in close. I have shot thousands of rounds through my SBE and have been completely satisfied, I highly recommend the gun.
The Berreta Al 391 or extrema are also good choices and have the adjustable stock, but I have no personal experience with it. I don't know anything about the SBE II except that it is ugly as hell.