Hardcover, softcover, digital? What is your preference?
I like 'em all, so it depends on the product. PDFs are terrific for my Gamer ADD. I have hundreds of game books on my iPad, so I never find myself late for work and staring at the shelf trying to guess what I'll be in the mood to look at come lunchtime (yes, this used to happen).
But PDFs aren't the end-all and be-all for me. I love the physical aspects of a book.I like being able to page through one at random. I like being able to loan a copy to a friend without feeling like we're breaking copyright law. Also I'm in inveterate bathtub reader, something I won't do with my tablet. So, there are plenty of RPGs I own in both PDF and physical form.
Hardback versus softback is less of an issue. I'm more about the contents than the packaging. As long as it doesn't fall apart, I'm good.