The difference in influence that these two figures have on Huck is most clearly demonstrated in the pivotal decisions they lead Huck to make.
Jim inspires Huck to loyalty, fealty and compassion. Pap Finn leads Huck to escape and deception.
In their characters, the two men present contrasting sets of traits. Jim is compassionate and humble. He tells Huck a story about how he learned humility from his deaf daughter when she was very young. He looks out for Huck and does not mention much of the help he offers to Huck. He acts generously. Huck recalls this behavior when he decides to help Jim escape from captivity (and these are all qualities that qualify as lessons for Huck).
Pap Finn is indignant. He is ruthless and proud, though he is also ashamed of himself. He is blameless in his own mind, yet recognizes the fact that he has squandered all of his cultural advantages in being a white male in pre-Civil War Missouri. The knee-jerk racism and generally defensive attitude toward all that he sees as superior to him combine to make Pap a highly judgemental person.
This particular quality stands in direct contrast to the lessons that Jim teaches Huck; lessons of compassion, patience and empathy.