10ga for geese. it's too heavy to carry for turkey hunting and it's too expensive for ducks... plus it's overkill, as is 3 1/2" 12ga. The 10 can be shot for a day of hunting while a 3 1/2" 12 can't because it kicks so much, plus it's prone to short-shucking in pumps.
if you've got a 3" 12ga already I'd go with the 10 and use it to goose hunt.
I own all the choices, and i really don't like the 3 1/2" 12 ga. I have a benelli SBEII and an 870. I shoot less than 10 shells through them during spring turkey season. To me it's a gun trying to be good for too many things at once, and it ends up being good at none.
The 10 is a better waterfowl gun (I have one in BPS) and except for geese there's nothing I'd want the extra power for.