Well, if it was me and the gun was strictly for chickens, the 20 gauge would get the nod. They'regenerally lighter and with most loads, less recoil. Personally, I use a 12 gauge with number....6 I think, but I've used a 20, and for most purposes, I'd grab the 20. However, if I was also hunting waterfowl, turkey or pheasents, I'd get a 12 gauge, just for the extra omph. Hope this helped