I will go on record that I am an absolute fan of the Bits and Mortar program, which provides a PDF of a book that you buy. Some of my favourite publishers, Evil Hat and Cubicle 7, participate in the program. Which means I have the hardcovers of the full run of The One Ring, while I also have all the books in PDF form. This is ideal for me: I play a lot online, and PDFs are easy to find stuff in when you're at the computer anyway. And I read most of my RPG books on my tablet, which is really convenient when travelling or just sitting on the couch.
So for me, the order would be: hardcover + PDF, PDF, hardcover, softcover.