There's certainly a lot to say about the aristocracy of Florence and Venice: I actually wrote an answer about the codification and institutionalization of the Venetian upper class that you can read here. I'm a little confused by your question premise though: what, precisely, do you mean when you ask "Relative to each other?" There was no real cross-border accreditation system, although the upper class certainly had a tendency to make a big show of in order to impress their foreign counterparts when they did interact. In Italy, for example, the Duke of Milan Gian Galeazzo Sforza was notable for his enormous Francophilia, maintaining a large embassy in Paris headed by his brother Lodovico and taking care that his representatives wore French clothes and generally looked impressive.