I've taken all of the exams, and in my opinion in terms of difficulty....
Real MCAT> Princeton Review Tests > BR Tests > AAMC Tests > Kaplan
Kaplan has some plug and chug stuff and lots of math that is good if you get a math based MCAT, but generally you won't.
In terms of what the actual test was like when I wrote...
Physics: A combo of the TPR tests and the AAMC tests, some really really easy questions, and then some WTFs.
Verbal: AAMC all the way. TPR has some seriously messed passages. I suggest EK1001 for extra verbal practice
Writing: Be able to formulate a Thesis, Antithesis, Synthesis and write "good". (For those that didn't catch the foreigner joke, it should say write well, I can say this cuz I am as foreign as they come, without the accent)
Bio: My best advice, pay attention in Orgo I, and learn the aldol condensation through and through. Know carbonyl chemistry cold. Also, the usual SN1 and SN2 stuff. Also, if you've taken a course in physiology, you're pretty much set for the second half of the TPR bio review. The bio on the actual exam had some difficult questions, but nothing IMPOSSIBLE. Don't underestimate the power of evolution. I had a passage on birds or something in Hawaii... Finished the other 6 passages in 40 minutes. Took me almost 15 minutes to decipher what the heck was going on. Orgo is generally a little gift on the bio section. (Thanks MCAT writers for asking me about hybridization!) But then again, there are apparently killer hard orgo passages out there. I had one of them. I straight up used "chemistry intuition" So don't get fooled into thinking you don't need to study reactions, because you do. But understand what it means when that little funky arrow points in a certain direction.
I would highly suggest remembering things that aren't so intuitive if you're not great at orgo like... the epoxidation of something... and then it's hydrolysis yields a trans-glycol.... MCAT Orgo LOVES LOVES LOVES LOVES.... did I mention LOVES?... stereochemistry. Pay attention to that stuff when you're studying. Don't just go through memorizing products and reactants. Know why things are pointing the way they are.
Good luck!