AirTran offers good prices between Philadelphia and many places via Atlanta or Boston (especially New Orleans). However, I agree with henecheta that they need a FF alliance to make you choose them over a major carrier where the service is better for a similar price. By the way, I flew Southwest a lot and LUVED that airline when I lived in Texas for the past seven years (before moving to Philly last year). I never really felt the "stampede" on SW which shows how subjective these impressions are.

AirTran has a FF program of its own that is similar to Southwest's credit-based program (rather than mileage-based). Has anyone used it yet? Is first-class on AirTran worth the small difference in price? That might make it worth the switch.