I bought several different books for MCAT prep (I have a habit of buying way to many informational books....I've got about 15 guitar books on my shelf, and only consistently use 3 of 'em) and after the first week, never looked at anything but EK and got a 31.
I never looked at classnotes, never looked at Kaplan ever again (seriously, worst book purchase I've ever made), only EK and practice exams on the MCAT website.
My advice is to consistently test yourself, not just after you've studied, but before hand and during also. You'll find you get a better idea as to how you should study after a few practice exams, and get a feel for the sorts of things that they try to use to trip you up. I loved EK for the way they specifically made a point of referencing tricky MCAT questions, and found several of the exact types of tricks on the real exam.
Good luck!
And don't be disheartened by poor performance on the practice exams (I don't mean stop studying cause you're fine, I just mean they often aren't the best predictors for how you'll do in the real scenario, at least for the EK practice exams anyway....I consistently scored about 5-6 points lower on the practice exams than I did on the real deal).