TPR vs. Kaplan?
Well, I took Kaplan, only b/c TPR refused to give me a discount even though I'm one of their SAT instructors--damn them!
However, my advice is this--the classes are most beneficial for the discipline they provide. Taking a $1200 class forces you to study for a minimum number of hours. For someone like me, I needed that set schedule. I needed someone to assign me homework and force 8 hour time slots on Saturday mornings for practice tests. Otherwise, I wouldn't have known to push myself so much. For this reason, I don't think there's much of a difference between TPR and Kaplan. Both will force a large time commitment from their students (which is what I believe you are paying for).
So, if you have the money, take a class knowing that it's not going to teach you everything, but it will try to prepare you for the format of the test and make you set aside x number of hours for prep and practice tests. If you are disciplined enough on your own, then save the money and study on your own. Very few of my Kaplan teachers knew more science than me, but they sat there and forced me to read those sections and tests along with them. Otherwise, I probably would have gone out with my friends and said "screw MCAT studying tonight." Try to think of TPR and Kaplan as a discipline regime, more so than a science teacher...
good luck,
poohbear