For personal travel, I always use the Ramada--the van service is extremely prompt, and the rates are cheap. I just returned today from a trip: I parked there from June 15-26, and the total bill was $87. The hotel is located at the Essington exit on I-95, just south of the airport. It's a 5-minute drive to PHL.

My company makes us park at Priority Parking (same exit off I-95, turn left at the traffic light instead of right for the Ramada) for business trips. The rates there are a bit higher, but they have valet parking and they also have an optional car wash service--they'll wash your car just before you return. That can be nice too, a real time-saver if you care about such things.