[Angst]

A cover is intended to bring attention to your book in a bookstore; to differentiate your book from the books surrounding it and to draw the potential buyer into picking your book up, and perusing it, and, hopefully, buying it. This holds on Amazon also, where your book is presented, with others, on "if you liked this book, you may also like these books" lists.

That said, both covers are very good. I would give the edge to the first cover as that was the one that drew my attention.

After looking at the thumbnails on Amazon, the second cover works better as a thumbnail.