I prefer reading digitally for everything except books with a lot of pictures. It's just such a better experience, especially with very large/heavy books. Adjusting the line spacing is a big one for me for comfort - I really struggle to read the smaller size of paperbacks because the squashed lines give me eyestrain (the larger "trade paperbacks" are fine). I'm also a minimalist/environmentalist and don't want to kill a tree, and I don't generally reread books.