We arrived at the Philly airport (from CT) at noon this past Saturday and the long term lot was full. Since we were parking for 10 days, I didnt want to pay $16 a day for the garage. The security guard was helpful and send me to a private lot south of the airport. Unfortunately when I got there, they only take reservations and they were full. The nice gal at the desk gave me a coupon for 25% off and directions to their lot on the north side of the airport.
The name of the company was Fast Track (formerly Avistar). We use them at Bradley airport in CT. Their shuttle to the airport was quick. We will see how good they are on the way back.
Luckily we were at the airport with 3 hours to spare as we were sure how bad the Presidents Day weekend traffic would be. So I wasnt in a panic.
As long as you are not going on a peak period, you should be fine with the long term lot but know that you have a lot of other choices.