I used to be an In-N-Out fan but Five Guys is now my new favorite new fast food burger joint. I think Five Guys gives you a good value for its price. The food is fresh and you can choose from a variety of toppings (from mushrooms to peppers) to add on your burger. Also, their fries are pretty good, though they are not as unique as In-N-Out's or McDonald's; I recommend ordering the seasoned ones.
Be sure to tell them you want a "little" hamburger or cheeseburger or they will give you a double patty burger.