Major in something that you enjoy. A biology major needs to take enough chemistry to pass the MCAT. A chemistry major need enough biology, etc.
When are you taking the MCAT? If you are taking the new exam in 2015 you will also need psychology, sociology, and a bunch of other "soft science" classes. If majoring in one of those subjects interests you then go for it. Just make sure you do well in the science pre-reques.
If Anatomy is what turns you on, then do anatomy. If staring a test tubes for hours on end while a reaction occurs, then do chem, organic, or biochem major.
Bottom line. You will get more out of doing a major you enjoy spending time doing. Don't do it just to pass a stupid test.
dsoz