I was very paranoid about this too, and so I took the kaplan class, bought BR books and all of examkrackers material. I have been able to compare the materials very thoroughly.
EK and TBR:
although I'm wary of people like meowmix that sound like EK sales very subtly trying to promote(doesn't matter if you are or not, but it's not unlikely, for evidence of how concerned EK is with what is said about them on this board, you can search previous posts and find founder cocky Orsay himself posting until people begged him to stop because it made them have second thoughts about his books)
get the EK stuff for verbal
for science if you learned it AND REmember it thoroughly then EK will do you good. (this is because EK is really only one guy, Jonathon Orsay, who wrote some stuff for Princeton and has a history BA, Just like TBR is one guy who wrote/worked for princeton previously; both saw they could make more on their own and so they opened shop to cutthroat premeds in a niche market without any serious competitors ("insiders" preparation (for evidence go to "What does Jonathan Orsay know about MCAT?" on the EK website) vs impersonal, big market Companies that allegedly ride on their name and care less about the merit of their product) and are successful salesmen, I believe, only because their materal is for the advanced student in mind (I think they know insecure below-averagers will go for what most people are doing), in that they cover things more indepth and EXPECT you to know the material off the bat, (their schedule recommends skimming, reading, rereading, doing practice problems, and a mini test all in like 2 hours [or so]) they provide the most succient/efficient/effective review, strategies and practice.
TBR is similar to this, except their science review is VERY detailed;I think too much. Even the author says in the classes he teaches that the books are for practice and ingraining strategy, and not for review (his lectures are review). The advantage to TBR books is that their coverage is very thorough and they have a lot of practice (EK sees this as a fault, that they're wasting time on things that aren't going to be on the mcat, etc), but if you've got time and really want to know you're stuff, TBR science review is good.
(the material of their books is really cheapo though, especially the paper, and only black and white; when compared to EK, which has the best material and color and is pretty lively especially with their 2 characters. So if you're a real cutthroat and don't care about a sort of boring book, but your score, TBR is, maybe the best but only if you combine a with a lecture if you don't have your material down. (their average published score is very high. I don't know if it's still true but at UCdavis, they guaranteed their students a 30, with their average scores being a 32!)
Kaplan: (I am unfamiliar with Princeton, but I expect the points I make will be applicable to both) They have expanded their online material significanlty, you can access all their "paper" materials online now, and they have added complete lectures online, and workshops/quizzes etc. IF you don't have your stuff down I think Kaplan is very good because, TBR/EK are one-man authors and so if you don't have your stuff down you're going to have trouble understanding because the authors are NOT great writers. (If you get EK and you don't have a good grasp of the material already, you'll find yourself sortof puzzled in some paragraphs or at cocky Orsay (sorry I think he is personality wise, it's not meant to degrade the material though) trying to teach you some science in a whole new "better" way, when you remember a little about the different way you learned it in the classroom and now you're completely confused; or )
 I strongly believe that Kaplan has the Best Written material and almost certainly has editors that focus solely on grammar/writing/english, etc. THis makes a HUGE difference in trying to get the material. therefore is easiest and best to review the material, especially now with all the different ways to concentrate on your weaknesses (re: dieselpetrolgrl) and do online workshops that help you in concepts that you really suck in.
although i've said many things that sound like they're coming from my own experience, much is from what I've gathered from some months of reading many peoples posts in the mcat section of sdn.
. Because at the end you have to make sure that you are comfortable with all the sections on the test.
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