Ahh the eternal Debate. Actually its more properly Trade Paperback v. Hardcover v. Massmarket Paperback. There is a debate going on at the ASOIAF forum about what people prefer. Personally I prefer Hardcovers, but sometimes they arent available, and sometimes cost is a factor, but I generally try to buy in HC if its not just a book, I'm taking a flyer on.

This post by Brandon Sanderson, author of Elantris, and Mistborn, gives the author's perspective on the debate.

The gist is that authors make a lot more on hardcovers sold than on paperbacks.