Any legal caliber will do its part if you do yours. Your part is to put the bullet in the boiler room at an effective range for your ballistics. My favorites are the ones I've killed with 30-06, .308, 12-ga, and .50 muzz. I'm a huge fan of the Barnes ttsx or tsx for a projectile. Those damn things are just f'n killers. I hear good things about the Scirocco II's by swift as well.