I shoot a Browning Cynergy camo 3.5" O/U. Killed a truck load of ducks and geese with it. Most likely my last waterfowl gun I will ever need. It's shot cases and cases of shells. Snows, Blues, Honkers, Mallards, wood ducks, teal, Gads, pintails, ring necks, bills, redheads, you name it, it's killed it, along with plenty of upland birds. It's a go to gun for anything that flies for me. Numerous others have shot it plenty too. Completely wore out a SBE in the same time period. This baby is just getting broke in. A true testament of just how much longer a good O/U will last over a auto or many pumps too.
I have a 3.5" Beretta 686 onxy Pro O/U also but have not shot anything but some trap loads through it.
I have a Remington SP-10 10ga auto I have had for many years, that I use of geese when they are the only game I'm after, but it has shot plenty of ducks too over the years.