MedSchool28, can you give a little more details about how the programs differ and if that relates to any particular goals you might have?
Do you have any particular things that you think you need to learn (eg really want to learn stats, how to do outcomes research, etc)? If it's about what will be the most useful and important going forward, I would say learning stats, datamining, and technology/EMR stuff, but I'm super biased.
I have colleagues and friends who did an MPH or epidemiology degrees before med school, after second year, and after school, often during fellowship. I think it all works out different ways, none of them bad. Incidentally, I don't think I know anyone who did an MSPH for whatever reason, but it is just less common.
If you are looking for something that will make you more competitive, nothing is more important than excelling at something, that is the key thing. It's less important what it is.