Philadelphia is probably the best airport for both festivals and rent a car from there.
But you might be able to hook a ride from someone else arriving at the airport as well. I know I fly in for RosFest to Philly as well. But I'm coming in Thursday night to get settled and play friday in the city.
But we might could pick you up if timing works right.
But you probably want a car for this area. Not very public transportation minded out in the venue areas.
Rosfest is closer in to Philly and would be a little easier taxi wise.
NearFest, you need a car or a chauffered service.