My preference is most certainly hardcover. I love a lot of classic books and hard cover just adds to the richness for me. On the go I like e-books (FOR THE MOST PART), mostly for books that would be overly cumbersome or heavy to carry around (medical texts, big novels, etc). Paperback for me is a complete and utter last resort that a hardcover does not exist (as with some of my favourite books (Dirk Gently, Discworld novels, ...On a Pale Horse and Good Omens).
I have recently acquires a copy of my OTHER favourite books The Hobbit in a very lovely pocket edition hardcover. It is very light, easy to read, small for storing AND is completely unabridged! I highly recommend it to fans of the Hobbit, or those who don't already own a copy of the book. It was really cheap too I got it for $15.95 on ThinkGeek. I would absolutely love a copy of Reaper Man, Soul Music, ....On a Pale Horse, and Good Omens like this honestly.