What is your favorite Harry Potter Book?

Half Blood Prince. There's not as much action in this one as others, but it's a gripping read on other levels. I like getting a look into the life of Tom Riddle and his transformation into Voldemort. Malfoy's struggle throughout whether to go through with his plan is very interesting as well, because although he always wants to prove himself, he ultimately isn't bad like his father. Harry's attempt to hold back his feelings for Ginny as well as clic Ron and Hermione clashing adds a good amount of emotional strength to the story. And there's the right amount of humorous scenes, like Ron drinking that love potion. The cliffhanger at the end left me with so many thoughts: Snape, good or bad? Who is R.A.B? What will their story be like without taking place in Hogwarts? It really set the stage well for an intense final chapter in the series.