If I'm goose and duck hunting at the same time, I use Blackcloud 3" #2's.
I use the same if I'm only goose hunting.
If I'm only duck hunting, I use Blackcloud 3" #4's.
I think 3 1/2 inch shells are a waste of money but that is just my opinion. I don't think they hurt anything as long as they cycle good in your gun. I don't feel they are worth the money if you are shooting decoyed birds.
If you are skybusting and praying for a kill, more pellets are always better.