#2 Shot definately! Oh, and buy a good quality shotgun shell. In my use, I've found that the cheap Winchester Xpert Hi-Velocity Steel Shotshells aren't as efficient as the best shells I've found...Federal Premium Speed Shok Steel Shotshells.
Federal Premium Speed Shok Waterfowl, 12 Gauge, 3", 1 1/4 oz, 1400 fps, #2 Steel Shot. (blue box)
I shoot a full choke and found that this shell is much much more efficient as to where im shooting.
Winchester Xpert Hi-Velocity Steel Shotshells, 12 Gauge, 3", 1 1/8 pz, 1550 fps, #2 Steel Shot.
I've cut open a Winchester shell and found that the bb's aren't all round, more oval and wierd shaped. Don't get me wrong, the winchester shells work but they wound more birds than anything.