... know absolutely NOTHING about cheesesteaks! Lol... Genos? I'd rather have a McRib. Jim's? Hasn't been decent since the 90's when they opened a couple more locations (they were awesome once upon a time though). Pat's is very good across from Geno's, but the best are, in order... Steve's Prince of Steaks (northeast) Chink's (northeast) and Tony Luke's (original location is better @ Front and Oregon in south, I believe). Don't mean to offend anyone, but I take my cheesesteaks seriously. Greatest food ever invented. They deserve to be respected.
Casual, nice dining? Go to Parc (corny French name I know) on Rittenhouse Square. The Continental is decent too (2 locations) but get there before the "hey look at my shirt and new haircut crowd" gets there or you might consider suicide.
I will agree about the cheesesteak comment, those are all quite mediocre at best, genos is terrible as well as pats ... If you are into mexican food .. dos segundos in northern liberties is a great spot to eat! have had it many times and never disappointed! Also Mexican Post is great, not sure exactly where that is at. Good Luck!