In my opinion the printed edition of a book is the better one, because it's more "natural", less stressful for the eyes, there is no "light" in the background of the page, and (imo) it's easier to keep your mind focused on what you are reading. I find the digital format tiring to the vision (actually much much more tiring than playing videogames), and i want to keep my "perfect" vision for the rest of my life( if it's possible).
Moreover, whenever you need to go to the next page, you either have to press a button or scroll the page (with your mouse wheel/directional arrows/finger whatever), which is not hard at all, but it's easy to misclick or scroll too much and lose the thread.
Iphones&co screens are too small, you have to change page too often and that's quite annoying imo
I have never tried to read from a Kindle or other E-book readers, i would like to try them and see if they are really better than pc/iphones screens.