Digital, unless I really want the book and it is only analog.

The analog form factor of books is IMHO much nicer, and I understand everyone who doesn't like digital books.

Stil, for me going digital beats analog:

• Having books always in my pocket, I never wonder what to do if I have to wait somewhere
• Going for work/leisure travel, always fully stocked with interesting reading material
• Learning from books and making notes? Digital makes it far easier
• I mostly read English books for learning and in my country one has to pay a heavy surcharge for English books

I also have to say, Amazon really earned all the critic it gets, but their Kindle apps and physical devices are awesome. It is easy to buy DRM free books and read/sync them with Amazon kindle infrastructure (send to device etc.).