Jim's 400 South St.
Being a displaced Philly native, I must suggest Jim's on South St. You can have CheeseWiz or real cheese. I like the American which melts through the meat and roll. I will be in Philly this weekend for a Jim's on Saturday. PM if anyone else will be there. BTW, the wife who is from Kentucky, will experience her first authentic Cheese steak. The food I was weaned on.