Which Kindle Case: Silicone or Book?

I'm really liking the Amazon Kindle, but can't decide on how best to protect/cover it.  I have both a book style case, and a silicone skin.  The book case affords more protection, and looks nice, but it makes using the Kindle feel more like holding a book, and defeats the purpose of it's thin, lightweight design.  The silicone skin isn't bad, but it doesn't fit snugly on the side.  So, which should I use? Or, should I give up the idea of using a case on it completely?