I posted pics a few pages back (probably a few months ago though) of mine--I have one small and a few large so you can get some idea of the size difference. I'm 6ft tall and definitely prefer the large. The small is a decent size, but the bag sits higher up on my arm pit and bothers me. In fact, I hardly ever carry mine anymore and have been thinking of giving it to my sis. The large is perfect for me, although it is a large bag. At the same time, though, I tend to travel with it or use it for textbooks, dance shoes etc---so basically I'm stuffing mine and like the extra size. I did give my sis one of mine and she's 5' 6"
I've never thought it looks too big on her.
Hope that helps a bit...