.410, 28, or 20 if kicking brushpiles. If just slowely walking and shooting as they sit, I like my .17HMR. Any bunny within 150 yards is gonna have a problem. Just gotta make sure you hit them in the head or you will have a mess.
Best gun you can ever use is a 22/410. It’s the best of both worlds. If ya see one sitting there you can shoot him with the 22 and if they are running use the 410. I have one and love it to death. Only gun to have if ya hunt rabbits.