The Benelli will be far more likely to continue to function in harsh dirty condtions. It will be lighter and will recoil more.
The Beretta will be heavier, will be just as reliable, as long as it is kept reasonably clean. (not always possible in a duck blind). The Beretta will have a bit less felt recoil because of the gas system and greater weight.
My personal peference is the Benelli M-2. I have no need for 3.5" shells. Any of the 3.5" guns will be less than 100% reliable with the lighter 2 3/4" ammo used most often. The 3" guns will be more reliable with lighter loads. I don't see the logic of owning a gun that will shoot the shells I'll use the least (3.5"), and have a less reliable gun with the ammo I'll shoot the most.