Kelsier. He is simply awesome. He is a skilled fighter, he is funny, he trusts others. He tries to help the skaa, and he has a consuming hate of nobles. He is psychopathic. He could have been a villain. At least two villains in Mistborn has the same goal as him. Quellion even bases his rules on Kelsier. That is the great thing with Kelsier: he appeared a hero, but his message, and his actions, were sometimes incredibly wrong. But he is charming, so everyone likes him. Also, he is hope.
And finally:
As for a fight, Atium could win it for Kelsier. Otherwise, he would most likely lose. But still, Kelsier is one of the greatest characters ever, so... in my book, he wins.