i love my gm=) its such a versatile bag for me. i love its size. i can fit anything i need in it! and when you don't have too much stuff, it looks gorgeous cinched and can be used as more of an everyday bag. i had purchased the mm at first, but switched it for a gm. i liked the size better. and while the mm looks a bit awkward when its cinched, gm has the nf slouch=)
i've also never had the problem of straps digging into my shoulders. i carry heavy things in my bag too..textbooks, macbook.. but i've never had the straps bother my shoulders.