Depends on what I'm doing and what the book is. Like the Lord of the Rings I'd rather listen to. But if it's Eragon, I'd rather read it. Also I can listen to it in the dark, while playing video games, یا doing math.
I hate audio books, for some reason I can remember and imagine things better if I read them myself. With audio books, most of the time my mind just starts wonder to other things and then I don't even know what it's going on in the book.