My choice would be The Original Hot Dog Shop (aka "The O" or better still, "The Dirty O") in Pittsburgh, original Oakland location only. Must have eaten hundreds (thousands? – no, I’m still alive) of them over 7 years of school at Carnegie Mellon. They were (hopefully still are) natural casing, crunchy from the grill. Had to have it with chili and cheese along with a basket of some of the best fries ever. There might be better dogs out there somewhere, but I had a lot of good times at this place.