Personally my most used and preferred .30 caliber is the .30-06. It can take on any game in North America likely any animal on earth if proper care is taken.
If I were going to hunt the larger animals (elk, moose, bear) more often a .300 Magnum would probably have some advantage over the .30-06.....but not much.
Even though I choose the .30-06, the most versatile and useful chambering is probably the .308 because of the number and variety of rifles that chamber this round. It performs at near .30-06 levels and can be had in any action type you could want (lever, pump, semi-auto, single shot, bolt) and can be had in a short action for those who prefer that action type. In a full length bolt action the .30-06 is the way to go, but for any other action the .308 has the edge.
