I use:
For trap/target shooting: Wally world value packs #7 1/2 shot
Pheasant/ grouse/ woodducks: #6 shot value pack ammo
Waterfowl: 3" #4 steel Federal or Remington
Canadian Geese: 3" BB or #2 steel Federal or Remington

I'm going to try out some of the Remington Heavishot this year for geese- its expensive, but I feel that steel shot gives pretty poor performance on the big honkers unless you are shooting them over dekes and getting them in really close.