20 gauge will lay the whoop a$$ on ducks and geese. Lower pay load, but faster follow up shots due to less recoil. If Browning, Beretta, or Benelli made a left handed 20 gauge I would be waterfowl hunting with that exclusively.
1 ounce load of steel #2's or if you want to fork out the ching, some hevi shot #4s. Either one wil stone a big goose to 35 yards with the right choke and the hevi shot 4's to a bit further. My nephew's girlfriend came out with us a few times in the early season and she did VERY WELL on Spet. honkers to about 35 yards max with my 20 gauge turkey gun re-fit for wing shooting with Rem. Nitro Steel #2's. I aslo have some of the Heavy Metal "turkey" loads, for whatever they're worth. I think they're junk for turkeys, but boy do they blister a big goose!