If you want to flatter the models, first shot has been taken too close. There is some perspective distortion and the skin texture is pretty much destroyed by the flash.
2nd looks a little flat, I suppose due to the direct flash.
3 and 4 are nice. And all of the models look great. But I suppose you could have improved the shots by using a bigger bounce for the flash. Looking at the catch lights it looks like you are shooting with bare flash.
I like #3 and #4 the most. For #3, I'd recommend cropping a little to remove the cleavage. The cleavage would have looked great (hey, I'm a guy ) if the boobs were entirely visible, but because they were cut off in the middle, I'd just crop them all up to the end of her hair.
The only suggestion I have with #4 as an ex post facto comment is next time try to not cut off her hair. Otherwise, it's an excellent photo.
) if the boobs were entirely visible, but because they were cut off in the middle, I'd just crop them all up to the end of her hair.