According to the most recent Harris poll:

The Bible.

From the article:

It came in first in a Harris Poll of nearly 2,513 adults but the second choice in the survey was not as clear cut.

"While the Bible is number one among each of the different demographic groups, there is a large difference in the number two favorite book," Harris said in a statement announcing the results.

Men chose J.R.R. Tolkien's "The Lord of the Rings" and women selected Margaret Mitchell's "Gone With the Wind" as their second-favorite book, according to the online poll.

But the second choice for 18- to 31-year-olds was J.K. Rowling's Harry Potter series, while 32- to 43-year-olds named Stephen King's "The Stand" and Dan Brown's "Angels and Demons."

Interesting, but I do wonder how many folks who claim it's their no. 1 pick have read it completely.

Cher

interesting info - thank you for posting it.

does it make me a bad christian if i say that the bible isn't my favorite book? (i've read it cover to cover)

No more than it makes me a bad woman to say that both LOTR and HP are my fave over GWTW (which I have NEVER read all the way through)?

Does favorite have to equate most valuable/cherished??

Well, I'm catching this a little late, but....
This is a very interesting topic to me.
I'm very much a girl, but I can't stand GWTW! I love LotR, HP, and the Bible (which I have NOT read completely through - good point Cher).

I don't think it's always fair when we're asked to pick favorites, as personally, I cherish different things equally, albeit for different reasons.