.270, hands down. They both shoot the same caliber bullet, but the case of the .270 is bigger, hence why the velocity is much higher (3060fps .270 vs. 2500fps 6.8). Also, given that energy will be greater as velocity of the same mass increase, the .270 has 2702ftlbs at the muzzle, where the 6.8 has a mediocre 1759ftlbs. These figures are from a 130gr .270 round, and a 115gr 6.8 round out of a 24" barrel, so if they were the same exact weight there’d be an even bigger difference in velocity, but slightly less difference in energy.
6.8 is often referred to as the “.270-Lite”.