pat's is better than geno's which is located right across the street. i like the cheez whiz. even though this is considered a tourist spot, i still see a lot of locals eat there.
Take from a local, go Pat's or go home!!! It's worth the inconvenience to go if you have time (place is always packed) - it's a Philadelphia South Street institution! FYI...my favorite is "A Whiz Wit"... ;)