Culvers, without a doubt. I almost chose Carls Jr. but since I haven't eaten there since I was eight, my opinion wouldn't be very good.
Anyways, onto my spiel about Culvers. I guess Culvers could be considered a 'medium'-food restaurant, but it is fairly fast food-ish. Their burgers are made for the order, so you don't get a Big Mac that's been sitting around for a half an hour. They've got excellent custard/ice-cream, better than DQ by a long shot. Another gret thing about Culvers: in every Culvers I've been in, which is pretty much every Culvers in southern WI, is clean; not like wiped tables clean, like 'just opened last week clean'. The food is great overall, and I've never had any problems with finding gross stuff embedded in my cheicken strips.
Yay for Culvers!