They seem to offer the freshest selection of veggies for burgers. I like their salads - especially the one with the mandarin oranges on it. Plus, they are the only fast food restaurant to offer a non-fried starch.
I think all of them use the freshest ingredients. It's hard to choose one because my family and I eat at all of these places and their food is fresh and wonderful. If I had to choose one I guess I would say Burger King.