Jax
LOL 18/2 in a 15-minute game. He got ganked at level one, was able to easily tank the ganker and still kill the blue monster and leave without ever going below half health with no one leashing for him.
Jax is so balanced. It's not like he can take an entire team and actually lifesteal more health than he loses while fighting five enemies at the same time. Oh wait, he can do that.