Tybalt and Benvolio are actually presented as dramatic foils. A dramatic foil is a character whose traits are the exact opposite of another character's, thereby serving to "highlight or emphasize" the opposing character's traits (Dr. Wheeler, "Literary Terms and Definitions: F"). We can especially see how their traits oppose each others' in the opening scene.
In Act 1, Scene 1, Benvolio is portrayed as one of the only rationally-minded characters in the play, as well as a peacekeeper. We especially see this when Bevolio rushes to part the battling servants, saying, "Part, fools! / Put up your swords. You know not what you do" (I.i.59-60). These lines reveal a great deal about his moral stance on fighting and his character. His choice to call the servants "fools" shows us that, with respect to his hesitancy to fight, he considers himself to be intellectually and ethically above the fighting servants. In addition, his line, "You know not what you do," shows us that, due to his character, he has morally judged the servants' desire to fight as both wrong and stupid.
Tybalt stands in great contrast to Benvolio in this scene. He proves to be the exact opposite of Benvolio in terms of both his quickness to fight and his quickness to judge a situation. When Tybalt sees Benvolio with his sword drawn, Tybalt is quick to assume that Benvolio is fighting with the servants rather than to notice that Benvolio is actually trying to stop them and establish peace. As we see in Tybalt's lines, "What, art thou drawn among these heartless hinds? / Turn thee, Benvolio! look upon thy death," Tybalt has assumed that Benvolio has drawn his sword to fight with the servants (61-62). Not only that, as we can see in his line, "Turn thee, Benvolio! look upon thy death," Tybalt's own motive for joining the fight is the complete opposite of Benvolio's. Rather than wanting to establish peace, Tybalt wants to fight to the death. These lines portray Tybalt as having a fiery temper and rash mind, which is the exact opposite of Benvolio's calm, peace-loving temper, and his rational mind.