The third one... I liked how there was a bit more mystery to it. Also, that's when Sirius was introduced The fifth book made me cry.
I know, Sirius is such an awesome character! I cried for a certain part of the fifth book too...I won't say what it was because it will ruin it for those who haven't read it.
I'm surprised at how many people liked the fifth book. It stressed Harry's emotions way too much. I know he's supposed to be all adolescent and stuff, but enough is enough. It lacked action all the way up until the final few chapters. But I guess some people always enjoy the recent one the most.
The third is definitely my favorite. I think that's when the series really started to get interesting, what with the introduction of Sirius and all. But I liked the fifth one as well, maybe because I waited so long for a new book. But I'm waiting anxiously for the sixth, but when it's all over, I suppose I'll be rather sad.
I loved Prisoner of Azkaban because a lot of great characters like Lupin were introduced, and I loved Order of the Phoenix because J.K. actually managed to get me pissed at someone who's not even real (Umbridge), but I gotta go with Goblet of Fire. Quidditch World Cup, the Dark Mark, the Triwizard Tournament, the Yule Ball... just too much goodness to say it's not my favorite. So, GOF gets my vote. Can't wait for the fourth movie by the way.
The fourth book! I just love the whole story ... I would've said the fifth, but it's just so boooooring and Harry's mad at everything, and Sirius falls into some veil thing and disappears and ... bleh.