The statistics from the American Association of Medical Colleges show that major does not matter in regards to be "better" for medical school admission. The ratios of matriculants majors are nearly identicle to the ratio of applicants' majors.
That said, there are some schools (at least 2) that have come out publicly and said they prefer science majors. There are likely others that feel the opposite way, and certainly plenty that don't publicly announce their preferences. However, on the whole, major does not matter.
Also, be aware that "specialized health sciences" majors have the lowest average MCAT score of any of the macroscopic major categories defined by the AAMC. source:
http://www.aamc.org/data/facts/2006/mcatgpabymaj1.htm
Finally, the advice I give to most pre-meds is that you should major in something you can be passionate about, something you'll enjoy. That's the most important thing since it doesn't matter to the medical schools.