Depends!
I like 2 shot for over decoys, but i usually use a BB or BBB for my last shot it is not very often you get a third shot but usually if you do they are a little ways away, and i like the knock down power of the BB and BBB. If you are getting the birds to land close to you, stick with 2's, but if they don't seem to be landing as close as you would like switch to BB or BBB. Kent faststeel is the best shotshell I have used in the past, and is worth the inexpensive price. But if you want some real awesome results duck or goose hunting try that new black cloud shot shell it is a real duck and goose buster.