Personality
Mercutio is extroverted, impulsive, and quick-witted. He is always ready for a fight and loves to make jokes. Romeo, on the other hand, is introverted, contemplative, and romantic. He is more likely to avoid conflict than seek it out, and he is often lost in his thoughts.
Views on love
Mercutio believes that love is a fleeting thing, and that it is better to enjoy it while it lasts. He does not believe in true love, and he thinks that Romeo is being foolish for pining over Rosaline. Romeo, on the other hand, believes that love is the most important thing in life. He is willing to risk everything for Juliet, and he believes that they will be together forever.
Role in the play
Mercutio is a catalyst for the events of the play. He is the one who goads Romeo into fighting Tybalt, and he is the one who is killed in the fight. His death sets off a chain of events that leads to Romeo and Juliet's tragic deaths. Romeo, on the other hand, is the protagonist of the play. He is the one who falls in love with Juliet, and he is the one who is ultimately responsible for her death.