Huck and Tom differ in living situations, personalities, and the way they view the world. Tom comes from a more stable living situation, while Huck is raised by his alcoholic father outside of the community. Tom is also educated, loves to read, and has an extremely active imagination. In contrast, Huck has little formal knowledge and is a practical individual. As was mentioned in the previous post, Tom is an idealist, while Huck is a realist. Tom also conforms to society's perception of African Americans and openly accepts the assumption that African Americans are inferior. In contrast, Huck questions the belief that African Americans are inferior and eventually decides to reject society after his experiences with Jim.
Pap's ramblings about the educated, free black man from Ohio are ironic because the black man is clearly more civilized and respected than Pap. Pap is an unsuccessful, deplorable alcoholic who believes that he is better than any black man simply because he is white. Pap's views are ironic because his character is inferior compared to the educated black man, yet Pap thinks he is better. Twain illuminates society's hypocrisy concerning the inferiority of African Americans through Pap's rant.
The main difference between the two boys is that Huck is more of a realist and Tom is an idealist. Huck is simple, uneducated, full of common sense and adventure, and a reluctant reader. Tom love to embellish things (his plans for helping Jim escape and his "gang" are two good examples), he has gone to school regularly since he comes from a more stable family than Huck, and he loves to read (which is where his romantic, idealist views come from mostly).
Tom also is adamant about the place of the black man in society, whereas Huck's views change on this subject based on his time with Jim on the raft. Had Tom not known that Jim had already been set free in the Widow's will, he would never have agreed to help Jim escape from his captivity at the Phelps' farm.
The irony of Pap's ire over the educated black man is that the black man can easily be seen as Pap's superior based on his ability to speak so many languages and his sophistication. However, Pap fails to see past the man's skin color. Therefore, Pap sees the black man as beneath him on the social ladder regardless of Pap's unpolished appearance, lack of education, and drunken behavior.