I would have to say 12 gauge buckshot. I will say though that you can take a good shooter and he could kill a deer with anything...take your average, lazy, 10 shot a year shooter and it doesnt matter what he uses...chances are hes gonna feed the buzzards pretty regularly. For instance....I have a neighbor that uses and it absolutely deadly with a 222 Remington....I dont ever remember him hardly even missing...let alone losing anything. On the other hand...I hunted with some folks one time that had a 16 year old son using a 7mm mag...he lost 2 in the same day with it. Caliber is basically irrelevant...its all about the shooter.