It depends on the situation, but for note, Rosalie is very polite and quiet. If she's running the booth or handing out fliers she's likely to talk to people with a smile, even if they're rude.
Marco, on the other hand, has a bit of a temper and a mean streak. He's typically friendly and won't go out of his way to be mean, but he's impatient and doesn't have much patience for people who get on his bad side (which is fairly easy to get on).
If there's a certain situation let me know and I'll tell what they're most likely to say.