TBH, it's kind of hard to "use" physical copies since my dominant hand is my right hand, and i can't really flip pages with just my left hand. But every now and then i like having physical copies.
So for the purposes of viewing...probably Digital.
I chose physical copies, but that's because I'd rather own something and be able to hold it. Being able to hold Ishikei's artwork in my hand is just awesome. But reading it on a big PC screen is pretty nice. Digital stuff is good for when you can't get a copy.
I prefer my actual reading books to be physical. I hate digital. However, I have the opposite feeling for manga. I prefer manga to be digital. The only exception would be omnibuses or anything that is a art book or is full color. I prefer those to be physical. I purchase manga in physical form to support them.
Physical all day every day. I always prefer my items to be physical than digital (games, manga, anime, etc). It just feels more right when you have the actual item in your hands.