I'm often perturbed when people use statistics yet mistake correlation for causation, and this seems to happen in many threads regarding this topic.
The OP's question "What do you think the best major to prepare you for the MCAT" is a question of causation. In other words, what major will cause me to get a higher score on the MCAT.
The statistics pointed out here regarding math and humanities majors doing well on the MCAT are not only for large aggregate groups, but are only correlative.
There is nothing inherent about majoring in non-sciences that leads someone to score higher on the MCAT. The simple fact is, just about every biology major, regardless of qualifications, and their dog takes the MCAT and applies to medical school. On the other hand, only a few highly motivated non-science majors take the MCAT and apply to med school. So of course the latter group is going to have a higher success rate on the MCAT and acceptance rate to medical school. If there are 50 archaeology majors applying to medical school, and 20 get in, that ratio is a lot better than 5,000 biology majors getting into medical school out of 50,000.
So pointing to statistics really won't help the OP. What will is descriptions of how specific classes within specific majors will help you on certain sections of the MCAT. Referring to statistics about majors and average MCATs is useless for the reasons stated above.
I think advanced biology courses help out a lot in the biological sciences section. Biochemistry, Immunology, etc might not help you overtly, but the classes get you into the right frame of mind in terms of thinking about questions. Also the more advanced biology courses are less memorization and more analysis, which is the type of thinking emphasized on the MCAT.
English ability, in terms of Verbal and Writing scores, is relatively inherent. I dont know to what degree I put faith in the Kaplan method of suddenly reading a lot of advanced humanities journals to improve your score. But if you read a lot outside of class, I doubt majoring in English will help you too terribly much.
The standard answer, and the correct one I believe, is that you should simply major in what you want. The MCAT is a one-time test. You don't want to have it be your focus for undergraduate studies. It's simply not worth it for a test. Take a bunch of varied classes and see what you like. I dont have any statistics to back this up, but I doubt your MCAT would change significantly depending on which major you chose. More likely, your own preparation for the test as well as your inherent intelligence will be a factor in your MCAT score. Also, if you major in something you like, your GPA will naturally be higher. GPA is generally considered one of the top 2 factors in admissions, so keep that in mind as well.
So I guess to summarize, take advice on "this major has a higher percentage of acceptance and a higher MCAT" with a large grain of salt, because they are corellative statistics related to large populations. And major in something you like. The MCAT is a test you will forget about promptly after you get into medical school, but the things you learn in your undergraduate major will stick with you for the rest of your life. So dont lose sight of that. Good luck to ya!
PS... I am a sciences/humanities double major and I like them both so I don't think I have any major biases.