I like print books to keep. I have very nice copies of all of my favorite books. I like to collect things and books are a great way to do that. Then I can very easily lend them to my friends.
However, e-books are so much easier to read on the go, I also find I can read them much faster because i'm not constantly forgetting my place. I use a kindle app on my iPod. I like to read cheap e-books of up and coming authors.
There's just something about the cloud and cyberspace that I don't trust. If the internet breaks down I don't want to lose this "collection" of e-books.
All in all, the cheaper the better. I can usually get hard copies of my favorite books for cheaper than I can get the electronic version.