In the east, I would recommend a guage, not a caliber. I'd say a 12 ga 3.5" would be the most versatile from cats and fox to yotes and even some crow hunting. I have found my Mossberg to be handy on any game living in this state from the occasional close-up groundhog to fall deer hunting. I even took 7 doves with my red dot scoped shotgun Tuesday evening. If he has his heart set on a rifle, then I would have to say 223 Remington, probably the most versatile round I have worked with. These two choices are why I bought a combo gun, now I have both in one gun whenever I go calling.