The review courses will only help you so much. It is important to have a solid knowledge of the basic sciences because, no matter how many tips and tricks Princeton or Kaplan tries to teach you, it is the basic knowledge (along with critical reading) that is really going to be tested on the exam.
You should also practice with materials produced by the AAMC. Out in my neck of the woods, Kaplan discourages students from taking full-length AAMC practice exams until almost a couple of weeks prior to the MCAT. This is bad. Begin practicing with AAMC materials as soon as possible. In addition to Kaplan, I invested eighty dollars in online AAMC practice exams. Their feedback was terrific!
To answer your question: I took Kaplan while my friend took Princeton, and we compared notes.
She noted that her practice exams were similar to the real thing. I thought that Kaplan practice examinations were one step more difficult than the real thing and that their "topical tests" and "section tests" completely missed the mark on what is tested on the MCAT. The Kaplan verbal reasoning questions were also a tad different than what I encountered on the real thing.
My teachers at Kaplan were (for the most part) friendly and knew exactly what was going to appear on the exam. There were easily ten or so questions that I would have been clueless about had my teachers not reviewed the concepts in class. Also, my teachers scored "fifteens" in the sections they tought; they could walk the walk. My friend who took Princeton thought that her teachers were boring and not very helpful.
Where I lived, Kaplan owned and opperated a test center that was open ten hours a day during the week and five hours a day on weekends. Princeton rented space on campus to host its classes.
If you were from my town, I would recommend Kaplan; however, the Kaplan and Princeton near you could be a lot different than the ones near me. Talk to people in your area. Their experience could be different from ours but representative of the sort of experience you would have.
Also, look into ExamKrackers. I do not know anyone who has studied with them, but it has quite a reputation on the net.
It all comes down to how well you can read, how well you can reason, how much (very basic) science you understand, and how many hours you want to put into preparation. My roommate took Kaplan, studied very little, and was upset by his score (still got into a very competitve school). My lab partner did not want to spend the money on Kaplan, so he spent eighty bucks on the AAMC tests, spent months reviewing them, and got into a top ten school (it didn't hurt that he was a surge-tech with a high cum gpa). Your score is really all about the effort you put into preparation. Learn all of the material on the official list of topics, learn to read and solve problems fast, and you will probably walk away from the exam with a score you are happy with...
Unless there is a fire alarm in the middle of your examination, the proctor calls time seven minutes early, or the sky falls...
