#1 has the best foundation, something solid with a pleasant backdrop of flowers at the bottom. It has probably the most natural and comfortable pose and expression. It also has good contrast, the better of the two smiles, and an appealing upward angle. The best overall image, to me.
I very much like the dark background of #2, but it doesn't contrast as well against her hair and shirt as the others (though #1 blends midtones at the crown). I think her hands would've been better off together or in a different place entirely, and possibly hidden. Add a smile (into the camera), and I think it would have been the best of the bunch...IMO.
#3 has a good pose and good backdrop, but no smile, and perhaps too much of an upward angle for my eyes.
I don't care for the angle of #4, and her hair may be occluded a little much. She also doesn't quite look like she's visibly "leaning" against the tree. My least favorite of the group.
I have no personal experience in taking candids or portrait shots; these are just my feelings.


