The characters I would compare in both books would be David and Sal. The similarities that both characters have would be their fascination with the people in their lives. For David his admiration to Giovanni was how Giovanni was willing to do whatever he wanted and not care if people judged him.
Sal’s admiration with Dean was how Dean is someone who does not fit in the world. All of his adventures that ye had aspired to do, that Sal felt he could not. Both characters begin the book with the people they admired. and it drives the main characters to do things for themselves.
The insight I have of both character is that they let the people they admire somehow lead their lives and decisions