Which book is best is as varied as the people using them. It is my opinion that a coctail works best. A mixture of materials from different sources will give you a broader perspective and exposure to different writing styles. The MCAT has several different writers, so your studying should keep that in mind.
In my opinion, no single company has the best text for all five subjects. As far as passages go, look for the best answer explanations. As for practice exams, look for MCAT realism. You obviously have to buy the AAMC exams first and foremost, but you might want to try at least one exam from each of the four major players (EK, BR, PR, and K). Variety will definitely help you deal with unfamilar passages on your actual MCAT.
Before you put down any money for MCAT materials, make sure they have tons and tons of passages. Doing passages is by far the most important thing. If the books don't have at least a hundred passages with well written, detailed answer explanations, you should look elsewhere for a more useful book.
