On the left is the US cover, and while I do like the color scheme, I don't feel like it quite works for me. I'm not a huge fan of the half-face phenomenon, and the weird shaped leaves surrounding her are odd. It also sort of looks like she has no neck and no body which is a bit disturbing.
The UK cover is on the right and oh my gosh, I love it. It's so surreal and beautiful and almost nostalgic, in a way. Just looking at it with its gorgeous colors stirs up emotions, and I adore the way the girl is portrayed. She looks raggedy and a little lost, which is a great contrast both to the lovely scene and the numerous YA books that have girls on the run while somehow wearing elegant dresses.
So as you can tell, the UK cover is the clear winner for me. Which one do you like better?