I am going to Italy this summer and plan to ask the waiters their favorite dish.
Answer on How do you say "what is your favorite" in Italian?
Perla answer is formally correct, but "preferito" is far more used then "favorito", and for sure it's used when talking about food; so, if you want to ask a waiter "what is your favorite dish" it's better saying "qual e il suo piatto preferito?" (use "suo", formal, since you don't know the waiter). "Vostro" used when talking in formal way to one person was in use till the 50s, now not anymore.