Even if you don't eat fast food or rarely do. I always liked Burger King for their burgers. Hardees for their breakfast offerings. My favorite would have to be a local chain here in North Carolina called Cook Out. They have chargrilled burgers and even quesadillas. Along with forty different kinds of milkshakes including Watermelon in the Summer and EggNog in the Holiday season. They even have banana pudding, blackberry cobbler, and strawberry shortcake milkshakes.
My favorite is Wendy's. Their food is great quality for fast food, and even comparable to or better than that of nicer sit-down restaurants. Their stuff isn't so greasy or rich it hurts my stomach (that is a huge problem for me), and it's delicious. I would pick it over Five Guys or Red Robin any day. Burger King would be my second choice, but I think Wendy's trumps them all and is in a league of its own.
I'm from the UK and I went the states this year and we don't have the same places you guys do :( but I loved Sonic, Hardee's, Jack in the Box, Arbee's etc... basically you guys now how to do fast food.