Pick up a few and see what feels good to you, an Ar10, M1a "prefer Fulton Armory", Cement, Fal, Just really depends on the money you plan on dumping into it as any AR10 or M1A can end up being the price of a ten year old car that you would drive daily to work, as well as the ammo you plan on shooting, whether it is grade, or not. One good thing about a fal, is its generally going to be able to eat machine gun ammo and over powered surplas that a M1a just can not handel, FAL food is usually that for a reason. Granit correct me if I am wrong.
No nato surplus should be overpowered, should all be loaded similarly and lower than commercial 308 loads