Whatever patterns the best out of your gun. It doesn't take much to kill a rabbit. I personally like large shot for small game hunting. Less pellets in the meat and they are easier to see. I won't shoot anything under #6 and prefer #4's for most stuff.
Paul
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I didn't climb to the top of the food chain to eat carrots! (Ron White)
6 shot. 4's in a 12 gauge tear em up pretty bad. I used to be fairly good at guessing the pattern on my old full choke shotgun and did not tear up much meat.
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Mess Chief, Ft Arroyo
"Tucson sweet. Best chili in the Saguaro."
I use low brass 6's usually but have even hunted them with my AA 9 shot I used for skeet and it worked pretty good if you weren't hunting extremely thick cover.