I love the art of a book so this is a really hard question.
Without a doubt, there was one chilling cover -- the one that pulled me in. And all it took was one drop of color.
Who designed this cover? Who was the artist? This is really frustrating. We talk about covers of Stephen King books, yet we don't mention the artist. And in press releases, it's hard to find the artist mentioned.
Publishers, you need to do better. Give credit where credit is earned. Someone or a group of someone's designed these covers. They pull us in. They intrigue us. And I don't care, but a lot of us DO judge a book by its cover at first. A bad cover doesn't necessarily mean we won't read it, but a beautiful, artistic cover can make me pick up a book faster than anything.