I really, really love the paperback. Because the boy on the front just looks so dejected and alone, and...sad. And I really like how the title is sideways and is in a really cool font, but what's with the tagline? No period or punctuation? I don't get it. Again with the face guessing game. I love that. One thing though. You can't really read the authors name because of the white color.
I like the hardcover too,(Look at the faces on the keys!) but it kind of falls flat for me. I don't understand the symbolism of the keys, but I really like the font. It's really cool, in a mystery novel kind of way.
So, the winner for me is the Paperback. (Couldn't you tell?)
Alright, I am very biased towards the key cover—I just have to get that out there. It's the cover I knew when I read it, and I absolutely loved the book, so now I'm pretty attached to it. I love the keys and how they look painted, but kind of faded on the edges. It wasn't until months after I read the book that I heard about the faces in the keys and actually realized they were there, but I think they're a really nice touch.
I just don't like the paperback as much. I agree with Megan on the sideways title and on the author's name. Having read the book, I know that the tagline ties into a big part of the story. My feelings on the whole cover, though, are kind of neutral—I don't dislike it, but it's not my favorite ever, either. (Maybe it's the blank gray background? I don't know.)
Anyway, while they're both good covers, the hardcover is my winner.