What Benvolio might think of Tybalt?
Well, they don't really say much to each other. They fight in the first scene, where Benvolio treats Tybalt with what seems to me a rather weary indifference:
What, art thou drawn among these heartless hinds?
Turn thee, Benvolio! look upon thy death.
I do but keep the peace. Put up thy sword,
Or manage it to part these men with me.
"Put up" means, "put it back in the scabbard". And, in Act 3, Scene 1, we find Benvolio making more or less the same plea to Tybalt and Mercutio:
Either withdraw unto some private place
And reason coldly of your grievances,
Or else depart. Here all eyes gaze on us.
Benvolio is the peace maker (his name means "friendly-wishing") and, though he doesn't seem tolerant of Tybalt's will to fight, he is still - rather gratingly - courteous. And that's all the judgement we get on Tybalt from Benvolio. However, Benvolio is present when Mercutio pronounces Tybalt deeply affected and pretentious:
Why, what is Tybalt?
More than Prince of Cats, I can tell you. O, he's the
courageous captain of compliments. He fights as you
sing pricksong, keeps time, distance, and proportion;
rests me his minim rest, one, two, and the third in your bosom! the very butcher of a silk button, a duellist, a duellist! a gentle man of the very first house, of the first and second cause.
Does Benvolio agree? Maybe. He clearly doesn't disagree enough to correct his friend. But he never says either way.