#1 looks noisy, like you underexposed and had to pull the subject up several stops, and the model is still underexposed. Also you've got some green tinge form light reflected off the grass. Some of the spots (pollen, bugs?) are so sharp they are a distraction. The dark background, bright foreground and underexposed subject create a very difficult overall image to work around. I would tighten the crop on this, maybe change ratio to 4x5, and offset the subject to the left side of the frame.
#2 I don't like at all. There's some shots where leaning backwards with the model's neck extended and curved back work, but this one goes to far IMHO. Also the smile is too big and the eyes too squinted. I do like the lighting on her face, highlighting of the hair and the creamy background. But then the direct sunlight on her arm, shoulders, neck and body is a bit much.
#3 is pretty good, but the model's skin looks plastic, like it's been overprocessed or maybe is out of focus? Unfortunately the light is very harsh and she looks pasted on to the background. The photo also seems a bit unbalanced, I would chop off the right side and also do this 4x5 ratio.
#4 I also think this is the best of the bunch. Pleasant smile, good expression, sharp, good crop. Except for the direct sunlight on the model's face, shoulder and breast, I would call this one perfect.