When atrempting to focus, the printed form is usually the most ideal since i find the mental reception much higher,
portability and the ability to keep backup copies is with the digital format, they don't weigh anything either, i sometimes travel between the village home and the one in the city for extended stays and find my books weighing down heavily, and because i can't always take them with me on the bike, end up without most books and have to get them sent to me so now i have some in the village and some in the city.
With all that said, when it comes to research mode, both printed and digital formats obviously have their advantages beause you can do 0.05 second word searches on the digital, copy paste, colour hilight without staining a book, and also email it in a milisecond. but with the printed books it's much easier to leave bookmark tabs and flip between multiple pages while not being lost in a myriad of buttons.
A huge hd touch projector like in minority report would allow a person to throw papers all over the place like on a real desktop though.
Anyways, when trying to concentrate on the Quran, i think most people woukd agree that the printed version in their favourite layout and format is the very best? No.