Firstly, I'll do the US versions. As I said in the cover reveal, I love how each one links together, through using the same fonts, same model, same dress, same place. In each one, all they have changed is the colour of the sky and what the model is doing, which I think reflects what happens in the novels. However, I would say that for the second novel, Dreamless, it doesn't fit the theme quite as well - I don't know whether that's because whilst the other two are mainly blue and purple, or the fact that the model is looking at the camera rather than off into the distance.
Although I suppose that I am slightly biased towards the UK version, I think it would win nevertheless. Although I love a lot about both versions of the cover art, I just think there is something more unique about the UK version, rather than the US version. I say this because there are a lot of different novels out there that just have a pretty girl on the cover - no others have the same - or in similar - style of the UK ones.