The 308 has a larger bullet diameter than the 270, however the case is a little shorter. (meaning less powder capacity) The 270 and the 30-06 are from the same cartridge case. The 300 win mag has a larger case again yet the bullet diameter is the same as the 308, and 30-06. Ballistically there is not much difference between the 308 and 30-06 untill you use a bullet over 165 grains. The 300 is the most powerful and typically is used with 180 to 220 grain loads. The 270 typically uses a 140 grain load. I have hunted mountain goat, moose, mule deer amd black bear with my 308. As far as accurate distances for hunting that is a serious matter of opinion on this board. Personally the distance where my shots open to a 4 inch group is the max range I hunt at. I believe that at that distance I can cleanly and ethically harvest game. That distance varies on the rifle. As for your question who makes the best 308 I have been assuming you were looking for a bolt action repeater for hunting. Is this correct or are you looking for a bench rest competition rifle?