Davy is a harder worker in my opinion. He trains insanely hard and his ranking and recent results show that. I think Nalbandian is more naturally gifted though, and at his best is a better player, although his best seems to only come out in spurts. I guess it comes down to what you believe, does the harder worker or the more talented deserve the reward. I think Nalbandian is the best player to currently not have a slam, but Davy deserves one as well