What is "best"? What do you want to do with your life? If you want to be an academic physician whose career involves research, teaching and clinical service, then doing research during undergrad, doing research the summer after M1 year, (maybe taking a year off after M3 to do more research), doing some research during residency & fellowship training and obtaining a faculty appointment after that is your career path. Being promoted as a faculty member will depend on getting research grants and publishing the results of research studies. If that's your trajectory, then going to a school with lots of research opportunities (measured in a rough way as Federal research funding by the US News and factored into its rating of the top research schools) is a good choice.
Some people try research and find that it is not for them. Some know from the start that they are most interested in serving patients in a clinical practice without any teaching/research responsibilities. Why should they go to a school that is going to be forcing research on them (requiring a thesis for the degree, or giving a degree with honors based on the quality of a research project)? Are there other schools that may be "best" for that student?
Best should be about good fit with one's interests and gifts, not what some group of people come up with to sell magazines.
Even if you have an MCAT of 40, if you aren't intellectually curious, interested in life-long learning and willing to consider a career that includes research, some research-intensive schools will consider you to be less than an ideal fit.