I'd say the gal on the right looks sharp, vs. the left's broadness. Both are attractive, but the expressions are strong enough that this seems more about personality than beauty. As someone said, the one on the right looks crafty/feisty, whereas the one on the left looks sort of vacant. Her gaze clashes with her mouth, which makes her smile look forced/fake --she's not having a good time.
Hope that's of some use!