Forget the other two down the street, just go to Jim's. The cheese steaks are the best, hands down.
The steak chef is a little testy (the cheesesteak nazi if you will), but the food is the best. The line often wraps around the corner, but don't be discouraged - it is definitely worth the wait. And while waiting, prepare mentally for your order. I like to say mine like a little mantra before stepping up to the sometimes toothless chef (I'm a plain, with fried onions gal).
Also, conveniently, they sell beer, which is the perfect accompaniment to a cheese steak. Oh yeah!