This is not a book about superiority of one type of person over another. Everyone has flaws in this novel, often very serious flaws. Jim and Huck are at least abashed to steal, yet they are willing to do so without much compunction, compromising on the idea that they will only steal fruit and vegetables that happen to be in season.
To posit that this novel is attempting to prove one type of person's superiority over another seems to miss the point.
I agree with the answers above that suggest that it the evaluation going on in the novel relates to moral perspectives, not types of people.
You could also use the words "slave" and "free" (or "white"), since Huck discovers that Jim is a better person than many of the others he meets along the way.
You could certainly say that "A person's conscience can be superior to the well-educated mind of another person."
Huck Finn stresses that someone's conscience can overrule society's teachings.
There is surely more than one way to answer this question. It may, perhaps, depend on what chapter you're talking about. But if this is for the whole book, I'd say there are two ways I could fill in the blanks.
- black person,white One of the lessons of the book is that Jim is at least the moral equal of a number of white people. He's surely morally superior to the Duke and the King, for instance. And he might even be morally superior to Huck and Tom.
- nonconformist, "civilized" Another lesson from the book is that the values of society are not always right. Huck doesn't go along with what society thinks he should do, but he is clearly morally better than many of the people who do go along with societal norms (especially in his treatment of Jim).