Why does Huck appear to be superior to Tom?

Huck seems to have matured more than Tom. Although Tom is imaginative, he is not as "pure" or "real" as Huck. Tom has a little more self interest and bias than Huck does. Tom withholds the information about Jim until the end of the story. Huck seems to have an internal value system that does not change. Although he looks up to Tom, Huck seems more of an altruistic character.