For doves or woodcock, #7-1/2 or #8 are probably just right. After all, that's what you use for trapshooting, which is meant to mimmick upland bird hunting.
For larger game (pheasants, ducks, rabbits,etc.) I prefer either #4, #5, or maybe #6. For geese I go for #2s. These are all standard 2-3/4" loads in 12-gauge.