What would be the best characters in Harper Lee's To Kill a Mockingbird to compare and contrast in an essay?

The best characters to compare and contrast will be character foils. A foil is a character with traits that are the exact opposite of another character's traits, and the opposing traits emphasize each other. Typically, secondary characters are used as foils against primary characters. Multiple character foils can be found within Harper Lee's To Kill a Mockingbird. Two examples are Uncle Jack, who is a foil to Atticus, and Jem, who is a foil to Scout.

Through Uncle Jack, we see several differences in parenting styles. Though not a parent himself, Uncle Jack has a significant influence on the Finch children whenever he is around for Christmas. In Chapter 9, one thing we see is that Atticus is a far more level-headed and patient parent than Uncle Jack. In fact, Scout teaches Uncle Jack a lesson in acting with reason and patience when she points out that he never stopped to listen to Scout's side the story concerning why she hit her cousin Francis. As Scout explains, "When Jem an' I fuss Atticus doesn't ever just listen to Jem's side of it, he hears mine too" (Ch. 9). When Uncle Jack finally does hear Scout explain what Francis said to provoke her, Uncle Jack becomes humbled and apologetic for having acted hastily in punishing Scout. Through this incident it's clear that author Lee uses Uncle Jack to show that, although Atticus is criticized for allowing his children to be too free spirited, Atticus's parenting methods truly are the best.

Similarly to Uncle Jack and Atticus, Scout and Jem also have opposing traits, yet they also swap traits as they grow older. In the beginning of the book, Scout has difficulty controlling her temper and readily lashes out physically anytime she feels someone is insulting Atticus such as by calling him a "nigger-lover." In contrast, Scout describes Jem as having a "naturally tranquil disposition and a slow fuse" (Ch. 11). However, Jem loses his temper the moment Mrs. Dubose calls Atticus "no better than the niggers and trash he works for!"; in revenge, Jem whacks off all of the camellia blossoms in Mrs. Dubose's garden (Ch. 11). Though Jem learns to take such insults calmly, after the trial, he develops an even worse temper than Scout. Both Scout and Jem are severely affected by the jury's guilty verdict. However, Scout is able to redirect her disappointment into lessons she internalizes about the treatment of others. For example, she reaches the conclusion that all people are the same and should be treated equally. Furthermore, when her third grade teacher, Miss Gates, speaks out against Hitler's treatment of the Jews, Scout recalls overhearing Miss Gates say to Miss Stephanie Crawford after the trial "it's time somebody taught 'em a lesson," which drives Scout to make note of Miss Gates's hypocrisy, hypocrisy that Scout very freely speaks out against. In contrast, Jem keeps his disturbed emotions bottled up inside, and when Scout brings up Miss Gates's hypocrisy, Jem flies off the handle, violently grabbing Scout's collar and shaking her. Hence, as we can see Scout becomes more level-headed as she matures, whereas Jem becomes so emotionally disturbed that he becomes violent. Lee uses this contrast between Jem and Scout to show the different ways in which the evil in the world can affect individuals.