For my work, I prefer read papers all the time, because I need to study how people resolve problems, and in papers I always find new experimental methodologies.
Books and internets only to take a general idea about a thopic.
I prefer to read on paper and reading books has advantages. I am able to grasp and understand content more easily when written on paper, I like doing sidenotes, adding paperslips with notes and so forth.
Anyhow, when in a hurry, and if available, I read essays and articles online or via PDF. Doing research for new publications online is more precise and easy than at the library (bibliographies often outdated), when found as data file I can browse easily and look up single words via word-search.
In Short:
If available, if book is available, if I need a lot: book and paper is prefered
If in a hurry, looking for single aspects, and if available: digital