1st: I really like the vibrant colors and use of the opposite bright vs dark scheme here. Her smile definitely explodes your creativity and fills the image. You made great use of the highlights in her hair.
2nd: I don't have any reaction to this one except that I don't like the unnatural balance of the windy hair and her face. Maybe it looks different in color, but this picture seems to draw attention directly to her face and her vibrant colorful hair is in such a way that it's not really part of the picture anymore.
3rd: Again she's not smiling in this one and is almost giving a face of disgust. Also, her eyes are reached to far to her left. Although, I think I understand the effect and affect you are trying to convey I don't agree with two elements which I think are... I wouldn't say negative but they do draw attention and mood. Having both of those (the eyes and the expression) is too much. Just think if she was smiling but looking that way you have a balance, and then you can continue outward to appreciate the whole picture. Or if she was not smiling but looked into the distance that is also a balance of.. "Hmm... what is he trying to capture? She's not that happy, but she interested in something... interesting."
4th: This is very close to the best one next to the first picture. Sometimes certain subjects are just best at simple lighting and background. In that sense you've capture all the features that make her stand out from the rest(if you had other model pictures to compare to next to her). It's bright, her skin and hair are the only contrasting dark colors, her smile stuns you and then you don't have any other choice but to follow to her eyes. Which I must say that one eye was beautifully captured. Not just because of the light spark, but the elegance of her hair working with her to only reveal the sexiness that comes with a playful and fun look. This may seem to some as a staple portrait standard; maybe even boring. Erica, however; made the shot with this example.
I hope I wasn't being too tough - I'm only a noob, but I hope I've helped you in some way. Thanks!
"No style as style, to use no way as the way, to have no limitation as the only limitation."