With only a few exceptions, I prefer Dead Tree Format for a variety of reasons. Economy is the major one: Printing is done in either Canada or the US, with the rare book in England. Most likely from local paper, from locally lumbered trees (Although I'll be really happy when Hemp Paper comes out!). Warehoused in local areas, possibly multiple places. Shipped by Canadian/US companies. Sold in bookstores that are local.
Ebooks just don't have that kind of personal reach, despite being quite nice and easy to have when you have an e-reader or laptop.
That said, I get impatient sometimes and will get a PDF RPG Book, and probably get the Dead Tree Format when I have spare cash later on.