Treasure of the Black Hole) is like naming your favorite child (he knows who he is).
So what is my favorite book I haven't written? I was thinking The Moon is a Harsh Mistress by Robert Heinlein. But to be honest, I haven't read it in years. And while I like Starship Troopers (also by Heinlein) it's a pedantic juvenile (what we call YA today) and not really "favorite book" material. (Forget the horrible movie. And I guess they're making another movie based on Starship Troopers. It will probably also be horrible.)
The book I have probably read the most is The Princes Bride: S. Morgenstern's Classic Tale of True Love and High Adventure by William Goldman. Why, because it's a fun read and I like its message ("life isn't fair"). And you have to read the non-story parts to get the full effect.
Yes, there's a movie version, and while I enjoy the movie, it's not nearly as good as the book.
So, I guess my favorite book is The Princes Bride.