Personally .308, five reasons, tried and proven, big enough for anything I hunt (up to Moose or Red Deer), acceptable recoil, if the SHTF it is a military caliber and something you may be able to scrounge on a battlefield and the vast majority of my shots are within 200 yards.
I've tried the magnums, kill in front cripple behind. Shooting one from a prone position can hurt. I sold my model 70 7MM mag. Only rifle I've owned that left me with a black and blue shoulder and scope eye.