If it's just for one person, go with the ravioli. If you'd want to share the app, the sushi is perfect for 2 people. It's too big for 1 person (IMO) to eat as an app....I tried that last time I was there and was left uncomfortable after the meal.
I would say the ravioli, however we are not sushi fanatics. When we were last there my DH had the ravioli as his appetizer and loved it, I however didn't think it lived up to my corn chowder soup that I was inlove with. I am not sure what I am going to do when we go in March because they don't have the soup on the menu anymore . That was one of the best parts about the whole meal.