Order of the Phoenix is my favorite because it is the book where you can see the characters go from children to teenagers/adults. However, I think Deathly Hallows is the best book. I love them all! Best series ever
In comparison to the rest of the series, Deathly Hallows fits in amazingly, ties everything together, and ends the books in the best way possible. The first one introduces us into the amazing world of Harry Potter. The fourth adds in the dramas of being a teenager and also the expansion of the wizarding world. And book six, thought considered boring by most people, is one of the best written books in the series. (Two and five just kind of suck.)
But the real winner of the prize is Harry Potter and the Prisoner of Azkaban. That book, on its own, could be an entire series of novels. It is by far the best book, movie, and moment of the entire Harry Potter series. There is no contest against that. It's just too friggen amazing to dispute.
I absolutely adore Deathly Hallows and Goblet of Fire... I adore all of them actually, but those two are my favorites. I do have to say Deathly Hallows probably wins though simply because it was the climax of the entire series, and it was brilliant!!!
I LOVE PoA but because I know it's going to rank high I choose OoTp.....I didn't like it at first, and I still don't like the beginning, but other than that I enjoyed the book thoroughly - I was able to feel like I was in the book most for this one! I also love DH... so these 3 are my absolute faves. : )
Prisoner of Azkaban or Goblet of Fire. No, I didn't choose the only two books Sirius was in, whatchoo talking bout.
...I haven't read OOTP since Kindergarten. I seriously got to the point where Sirius dies and was like NOES and threw the book against the wall and haven't touched it since. I've never read the end, seen the movie, and to this day I can't remember what happened in that book. I guess my mind blocked the traumatic event xD
I loved them all, especially PoA, because Harry had met Sirius and Lupin, his dad's two best friends and knowing that he could go and live with Sirius and be happier, well, I loved the idea. And Half-Blood Prince is up there too, due to its wittiness. And Slughorn just cracked me up.
But all in all, Deathly Hallows was my favorite regardless of the over-whelming sadness it brought because finally, the one force causing the world to nearly crumble was defeated due to the lack of love, friendship, and loyalty. (but we all know this, since Dumbledore said a million times--it never gets too old for me though.)