You appear to be well informed on this issue. I have had cheesesteaks (or, as many Pennsylvanians call them, "steaks") from Jim's on a number of occasions. Your reference to the "rebuild" suggests that you are aware of the fire at Jim's a couple of years ago. My understanding is that it necessitated a complete rebuild. I have not been there since that time. I assume it is still at the bottom of South Street, where it always has been.
I like Pat's steaks as well. I think Pat's has a couple of locations. The one I most often frequent is the one in Reading Terminal, which is one of my favorite places on Earth. If you can't find a particular type of cuisine in Reading Terminal, chances are it does not exist.
The other cheesesteak purveyor you see named most frequently is Geno's. I can recall having a Geno's steak, but I do not specifically recall whether it merited ranking on par with either Jim's or Pat's. Perhaps others here with knowledge of the subject will weigh in.
South Street is just great. Heart of the Italian Market. Some really good restaurants (Ralph's and Palumbo's Nostalgia come immediately to mind), A fantastic cheese and olives shop (Gaudio's). And Fante's, a kitchen store that looks unimpressive from the front doors on South Street, but which goes back and spreads out impressively. I have yet to come across a kitchen store that matches it. They have every kind of kitchen gadget known to man.) Finally, some really great Italian bakeries. Isgrow's is my favorite. Their cannolis are made fresh and they are amazing.