I'm such a lazy reader, but when I do I kinda prefer the printed version so I don't have to worry about battery. Ideally I want a printed PDF so I can just throw away the pages I read (A big waste yes).

As @sportebois said, it depends. A book teaching an idea - I'd like it printed. A reference type book - PDF to search. As much as we have iPads in the house, I'd prefer to read on my laptop / 2nd monitor. Walk throughs / guides about a specific framework - web.

In my opinion (but the number of answers is limited), the option "both" is really missing. I like to think I'm not the only one that like a print copy for "couch potato mode" reading, an epub to read on the go, and a pdf to search later in (in my experience, I haven't yet found an epub tool where search is as efficient than in pdf tools)

So I'd really choose the "give me all of them" choice ;-)

In the past few years, I use only printed literature, mainly. Or I look completely in digital form on the site freebooksummary.com/mother-to-mother-important-qu… which is very well made for this, it turns out very conveniently. In addition, there are just a huge number of books there, and you don’t have to look for all the necessary material from different sources, because there is enough of everything here