I tried both of them on and found the MM slightly too big on me (5'2") and PM almost too small...but I think I like the PM better. If I want a bigger one then I would go with the BH.
I've tried both of them on. I am 5'3" and I like the PM better. But if you have a lot of stuff, the MM should be fine as well, just a bit too big for my liking but not overkill.
personally i choose the PM. I dont carry THAT much stuff and im 5'9" so perhaps the smaller bag might look weird, but i like it. If price is a dilema, go with the cheaper one