Based on conversations between Romeo and Benvolio in Act 2, Scene 1 of Shakespeare's Romeo and Juliet, what differences between the two characters do we see?
A conversation between Romeo and Benvolio does not actually take place in Act 2, Scene 1. On the contrary, Romeo actually only has two lines in this scene, and, instead, a conversation between Benvolio and Mercutio takes place. So perhaps you meant to ask about Act 1, Scene 1 in which we see Romeo and Benvolio conversing about Romeo's broken heart over Rosaline.
However, one thing we do see based on the things that Benvolio says to Mercutio about Romeo in Act 2, Scene 1 is that Benvolio strongly disagrees with Romeo's take on love. Romeo sees love as a powerful emotion that he can allow himself to be overtaken by. Benvolio, on the other hand, is far more practical and wishes Romeo would gain more control of himself. We especially see this internal conflict between Romeo and Benvolio when in this scene Romeo climbs the garden wall, claiming he can't possibly return home when his heart is here at Capulet's house. In contrast, Benvolio is quite put out by the fact that Romeo has disappeared in pursuit of his love interests. We see Benvolio ridicule Romeo's behavior when he states that Romeo has hidden among the trees to nurse his amorous feelings in the night. He also states that since Romeo's "love is blind," his love is best hidden in the night, as we see in Benvolio's lines:
Come, he hath hid himself among these trees
To be consorted with the humorous night.
Blind is his love and best befits the dark. (II.i.32-34)
However, we even more strongly see the differences between Benvolio and Romeo with respect to views on love in their lengthy conversation in Act 1, Scene 1. Here, Romeo goes on and on about how brokenhearted he is and how much he feels that love is torture. Romeo clearly believes that it is perfectly fine to allow oneself to be carried away by one's emotions. However, Benvolio is far more rational and sees things differently. We especially see this when Benvolio begs Romeo to listen to his advice and forget about Rosaline, as we see in Benvolio's line, "Be rul'd by me: forget to think of her" (I.i.227). Benvolio is telling Romeo to use his rational self rather than his emotional self. However, Romeo refuses to be counseled and only replies that he can't possibly forget how to think.
Hence, one significant difference we see between Benvolio and Romeo is that Romeo is irrational and prefers to be guided by emotions, while Benvolio is far more rational, preferring be guided by sound thoughts.