AK-74 or M4A4 or M4A1-S??

AK solely for damage ANY DAY. It's superior and only weapons it might have a discussion against could be AWP which offers a single hit kill not only to head but also body. As of the M4 family, i'd choose the A4, i think it had a slightly better firerate and more ammo. If you're a seasoned player, the recoil control will be no issue.