If the PDF is made from a datafile (Green Ronin, White Wolf) and its sold at a discount (even 1/3 off), then I prefer PDF. I can print out a copy at staples for the difference and get it spiral bound, and if heaven forbid something happens to the book, I can get it printed out again for that same cost. And if the game is long out of print, I can print out copies for everyone in the group.
If the PDF is a scanned in copy of the physical copy and it is not sold at a discount (I'm looking at you Wizards), then I prefer the print. But I am usually not happy (and completely disappointed in Wizards' case) about that.