If 10 different people respond, you will probably get 10 different answers! lol....
For an all round load, I like 2's. Early woodduck/teal, 4's will do just fine. 2 3/4", 3", or 3 1/2" really makes no difference to me. I have all lengths. IMO 3" is ideal. Kents, Dryloks, and Rem Nitros is what's sitting on my shelf now. I only shoot steel, shoot'em when there supposed to be shot, and steel will work just fine!
For geese, I like BBB's. Before I moved here, I shot T's and they worked great, but I'm not sure if T's are legal in TN.