Tom Sawyer is a leader with a strong imagination, a penchant for passionate speeches and wild antics, and a gifted liar. Tom comes from a more stable background than Huck Finn, which may contribute to some of the outlandish ideas he has. Tom is not worried about being kicked out of his house and presents a rather supreme confidence.
Much of his confidence, however, comes from his willingness to engage in fantasy. In this novel, this willingness leads to a bullet in Tom's leg.
Tom is a product of the very “civilized” society Huck is escaping from, and eventually learns to reject.
Like Tom, Huck often resorts to lies and subterfuge, but he does so for practical reasons. Unlike Tom, Huck experiences a crisis of conscience that helps to define his character.
Huck is an imaginative problem solver when it comes to practical problems, yet he is not as capable of overcoming or setting aside moral issues. He is torn, often, between society's stated code of conduct and his own sense of what is morally right.
Ultimately, Huck decides to break free of society's moral constraints to do what he feels is right in saving Jim. Before this point, he is remarkably constrained, refusing to abandon the King and Duke despite the fact that these two frauds are not his real friends and do not have his best interests in mind.
Huck's development contrasts Tom's lack of maturity. Early in the novel, Huck begins to feel the pangs of conscience which never occur to Tom. When Huck finds Jim on the island, he is already beginning on the path toward moral maturity and a break with conventional social mores.
He fully recognizes this idea, though he needs time to come to terms with it. We see his conflict, his turmoil, and his awareness when he discusses he decision to side with Jim early on.
People would call me a low-down Abolitionist and despise me for keeping mum—but that don't make no difference. I ain't a-going to tell...
Huck can be seen as being more isolated and uncertain than Tom, with a greater sense of what his own actions mean to others.