Paris is guided more by politics and reasoning, while Romeo is guided more by passion and impulse. Because Paris wants to marry Juliet, he sits down with her father to make the arrangement. This was much more traditional of a way to arrange a marriage in that time. He is related to the Prince and the Capulets are a wealthy family, so the arrangement is probably somewhat motivated by those facts. Romeo, on the other hand, does whatever he wants to and acts impulsively. He sees Juliet, falls in love, and marries her without asking permission or thinking through the potential consequences.
