My advice...
I took a Princeton Review course one summer, after I had taken the MCAT once already...my score went up 6 points from the last time :shock: I had Kaplan books too from a friend...and I honestly thought the PR books were much better (for the $$ you have to pay for the course, I think they were more worth it). They were more comprehensive, had more examples, covered more material...whereas the Kaplan books seemed to be best for a crash course a month before the exam.
Also, take as many practice tests as you can get your hands on!! NOTHING else will help you more. Take them from DAY 1!! Even if you think you don't know anything. The MCAT site has actual tests you can download for a fee as well... I printed them all out and went thru them twice.