Poll: EBooks or Paper books for tech reading?
See additional discussion here: https://news.ycombinator.com/item?id=32888730
Paper books are also easier to rotate so that landscape and portrait style diagrams are easier to manipulate.
Having said all that, I like both formats for their advantages, and hate both formats for their disadvantages. So I sometimes have both formats available simultaneously, and use the most useful one for me at that particular time.