I personally prefer reading books rather than watching the movies. Books offer me the possibility to imagine the characters and the whole plot the way I want and, on top of that, the action seems more realistic and engaging. I do not like the movies that pretend to be adapted after the books - they do not contain the action from the book and, apart from that, the characters are always... strange. Not to say that they destroy my perception of the book in question. For instance, Harry Potter was extremely... plain. The action in the book was much more interesting (except the 5th book, which was a total mess) and the characters seemed more animated.
Some books make great movies, but there are only a few such cases. I like Pride and prejudice, with Keira Knightley as Elisabeth, this was one of the few movies I really liked!