Since discovering Potbelly, I will not go anywhere else for a quick sub-style sandwich. They just do everything better then Subway or Quiznos, and by a large margin.
The meats and vegetables are of better quality and fresher, the bread tastes better, the extras (drinks, soups, chips, cookies. shakes) are tastier and more interesting, and the people are nicer. I have found this to be true at several locations.
They also allow local musicians to play in the restaurants on some designated days. It's a nice thought, but I don't really think it adds much to the restaurant. Points for trying to reach out to the local community, though.