dpends, really. if you wanna kill zombies or robots, hiding behind doors and walls, you go with the 762. if you want max tissue rupturing, go with a slow twist 223, a 1/12 or even the origional 1/14 , with a 55 grain hollow point.
Very messy.
this is why the russians switched to the 545, had a better tissue damage/kill ratio as a percentage, than the 762. but that was before urban warfare, kevlar, bullet proof vests. they did their tests on the ammo from 50 to 300 yds, in open fields, probably on dead pigs, or Christians they pulled out of the Gulags.