Who else, Rorschach. Though the question of why is a slightly more difficult question to answer. It's because he views the world as it should be, there's good and there's evil and evil must be punished. Also, he's the only character who reacts to Veidt's plan as a normal person would, with disgust and anger. He realizes that the ends don't always justify the means; especially when the means are the murder of millions of innocent people. The fact that he's a vicious psychopath is another reason why I like him. I've always liked the idea of someone who's more like a predator that eats the other predators. I also enjoy his deontological worldview(morality based on strict rules). "Never compromise, even in the face of Armageddon." -Walter Kovacs
Plus, he threw a super villain down an elevator chute. How can you not live that?