i sometimes wonder this myself, last time was in Red Dead Redemption.
Sundance Kid, 4 kills
Jesse James, 16 kills
Me, 1850 kills
I wish there would be an action game with a somewhat realistic touch to killing people. Even in Red Dead, Marston could have just shot everyone in the leg or use non lethal force to solve situations. But rarely in games the non-lethal or just wounding an enemy is a valid option.
Anyways, in pure human kills i say Red Dead since most of them are story related.