Book 5 is my second favorite too, but it's really really close after book 3, which I love so much because of Sirius and Remus and we get glimpses of how they were with James while in school. Actually, some days I love more book 3, others I love more book 5 *grins*

I like the darkness in 6 too and the characters grow a lot and Ginny quite rocks there.

*waits for you to see the movie*