I think in the lighter pastel colors that the PM looks better. I purchased the Givre Alma in the MM size last summer and wished I had chose the pm. The darker colors like amarante are easier to pull off in the MM, jmo. I am 5'6, 118 lbs for reference.
I'm 5'3, size 4/6 and I prefer the MM size. I love the MM size.. But I just saw it today and I think I'd go for the PM size for this color.. Although I found the PM size too small.. I guess it's better to try both sizes so you get the feel of it..