Digital all the way for me.
Using a 12.9" iPad pro sitting on a stand takes up near zero bench space, allowing for more room to layout pieces and the model.
Can also zoom in on any section on the screen.
Posture is also improved as I am not hunched over looking at the book, the instructions are at eye level.
Build speed is also better as I can advance with a little flick on the screen, not turning a page.
When I got 42100 delivered the digital version wasn't available yet, so I used the book for a couple days and it was a hassle, as soon as I got it on the iPad it all became much easier for me.