Bolt action 308. Match grade factory ammo available, surplus cheap ammo available, hand loads can get you competition level accuracy in the right gun. Also, much accurizing can be done to a bolt action yourself. Glass bedding, trigger tuning/replacement etc. Bolt actions actually come out same weight, maybe even lighter with a heavy barrel than the Ar-10 platforms. and the AR-10's lose 100+ fps to a bolt action, everything else (ammo, PSI) being equal.
Lastly, there isn't much that the 308 can't do and do well.