I use a computer extensively for reading academic material, and a Kindle for books. I find that the Kindle screen is too small and too awkward to navigate for textbooks, but is easiest to hold. (I have the simple model, where entering text is very, very slow). A full sized tablet (not mini) is better, and a laptop works well - I can change position, the screen is large enough to see the material, and search functions are built in (which is useful). If I want to read a paper thoroughly, though, I tend print it out.
But doing it on a laptop requires more dedication than on the printed page, because right next to the document you are reading is your email, and web browser, and games, and social media, and all sorts of other distractions.