Im sorry to confuse you further, but I disagree with some things the above posters said.
Let me start of by saying: I do not think the p/f masters will hurt you, as this is the case for several masters programs. However, it also wont help you in terms of numbers (something you kinda need help in). So I would say it depends, how badly do you want a mph? Are you trying to get into top schools? What is your MCAT? If you are doing the mph just to impress, then maybe an SMP would be better.
Now, for the stuff people said above.
One person said mcat is the most important, another person said that mph is not important. Here is the truth: the most important thing is a story. Story story story. With thousands of applicants every year, this is the only thing that can make people stand out (Unless you have a 43 mcat). So, will an mph help? Only if it fits in and strengthens your current story, with the image that you will sell to medical schools. This requires thorough analysis of your background and narrative. For example, someone who grew up in a neighborhood with tons of pollution and grew up fighting for his communities health regulations but realized that he needed an education to effectively do so would benefit greatly from doing an MPH. It would strengthen the story. What you need to do is prove that you are not doing it just to impress schools.
Note: everyone has a story, not just the rags to riches kids. Its just a matter of being a good writer IMO. PM me if you wanna ask about specifics.