I agree to some extent with those who posted above me. Do it if your interested in it as being part of your career...not because you think it will help you get into medical school as I doubt it will make up for a bad undergrad.
To show what I mean, I do not know how allopathic schools figure in graduate work as I was unable to determine how they handled my graduate work, however, I do know that osteopathic schools do add the credits from graduate work into an overall GPA:
This is a cut out from my AACOMAS applications, where they calculated an overall GPA of 3.21 by combining my undergrad and graduate coursework. Assuming that allopathic schools dont give any more credit for graduate work than the osteopathic schools, I think its safe to say that it wont really hurt you to do it, but at the same time it wont help you anymore than going back and repeating courses from your undergrad.
To answer the OP's original question though, from my experience in graduate school, which wasnt for a MPH, but a Masters of Science in Microbiology, graduate school is what you put into it. I am not sure if a MPH is thesis based or not, if not, then I can see it somewhat mattering where you go and from what I have seen from people who pursue an MA in biology, its not really anything different than an extended undergrad and can be considered as easier than undergrad due to a lot of schools placing lower requirements on graduate students for the number of credit hours needed to reach full-time student status. But, if its thesis based, the quality of your work/degree is dictated largely by the quality and quantity of papers you put out.
I would also advise against doing a graduate degree if your planning on only taking 1 year off. If the degree is thesis based, you dont graduate until your thesis/research is done and written up..which can take a long time if you have other things going on..or your graduate advisor says, "I want you to take X-class next time its offerred"...and your stuck there for another semester/year until you take that class <---this actually happened to me and made me stay in my program for an extra semester... Atleast with post-bac, you pick your schedual.
