  In my opinion, Huck and Jim are both heros in this novel. Huck is a hero in a sense that he decides to go to hell to save Jim, which was a huge decision to make at such a time in the South. Later in the novel, Jim becomes the hero when he sacrifices his freedom (or so he thinks), the freedom that Huck has worked to protect, to save Tom's life.
Both Huck and Jim have their heroic moments by making huge moral decisions. They both have to decide whether or not to do the right thing, and the fact that they both end up doing what's right makes them both heros. Sorry, that made no sense...talking about stuff like this confuses me sometimes; I know what I want to say, but it just doesn't come out right! 
