1st study: Looks good, minus the chin doesn't fit the rest of the facial features. Everything else is great.
2nd study: Really good, I believe the (my right eye) is a bit high though.
3rd Study: Again, the chin doesn't fit the face, but the rest is great.
4th study: The neck is way to long, the face is fine.
5th study: I'm assuming this was meant to be a cartoon, in that case it looks very well. If not meant to be cartoonish... the features are way off from realistic.
6th Study: Simple and beautiful, my favorite.
7th study: seems a bit too much cartoonish mixed with realistic, I'd work out the proportions and decide where you're going before finishing the sketch.
8th study: Very pretty slightly anime.. or cartoon style little girls face. I like this study as well.
9th study: Sort of like a hybrid anime style... mixing realism with the typical anime traits (slight chin, large mouth and eyes) yet the heads shape, and features are done very realistic. It's a very pretty effect.