I am a little bias (I teach MCAT prep for Kaplan and I'm a former Kaplan student!) but this is my take on the situation. First if you already have a good science foundation--take Kaplan. There is a lot of strategy, great problem sets, and good overall review of material. Princeton Review on the other hand, has a tendancy to spoon feed material...which is great if you need to relearn, not review. Now if you are in Philadelphia and you decide to take Kaplan, try to sign up for a course that meets at the University of Pennslyvania. I used to teach there and I took the class there. In general, they send the veteran teachers to teach on campus and keep the less experienced rookies at the center. If you do take Kaplan, learn to spend a lot of quality time in the review library. That's where you are going to see you scores jump. Lastly, Kaplan by far has way more actual problems/mock exams/additional resources like flash cards, CD roms, and workshops than TPR. Although, I do feel TPR works very well for some people. Either way, good luck and if you have any additional questions about Kaplan...feel free to email me.
