Are we talking gauges or guns?

The most versitle would of course be the 12 gauge... as you can use 3" or 3.5" BBs for field geese or passing divers and switch to 3" or 2 3/4" #3s for timber shooting. I personally do not use a 3.5" gun or shells for waterfowl hunting as I don't see the added utility is dropping yet another $1500 plus ammunition into my already over allocated waterfowl budget.

The 10 gauge is the king supreme of the goose fields and doubles nicely as a passing duck gun. I have hunted in some nasty swamps as well as the green timber of Arkansas and I would not want to tote a 10 gauge through it all.

A 20 gauge is sweet and light and has plenty enough power with the right shells and within proper range. For wood ducks and teal... its awesome and I use a BPS 20 gauge in small waters for mallards and blacks myself. Don't need a 3.5" shell to shoot a duck hovering at 25 yards.

As to the gun itself.... it needs to have three things: 1) Boom, 2) Boom, 3) Boom.

And of course it needs to fit you well... I use mostly my old 870 Wingmaster Mag, or a Beretta 390 Silver Mallard. I am however thinking about trading in the old 390 for a Benelli M2... I'm squirreling away a few clams as we speak for it.