Gah! Can't - choose - too - good! AAAAHHH!!!
They're all so good, I can't have a favorite! Sorcerer's Stone is great, introducing all the characters and this innocent little Harry, Chamber of Secrets reveals so much, Prisoner of Azkaban is amazing, with Sirius, Buckbeak, and such cool parts! Goblet of Fire is great, with the triwizard tournament, and of course Voldemort coming back, Order of the Phoenix, well, is great! And the movie cut out a lot of parts, but it went so smoothly! Half-Blood Prince is amazing (and I can't wait to see the inferi part in the movie!), and the Deathly Hallows, well, it's an amazing ending!
All of them are so amazing, choosing a favorite would be like...choosing which kidney to keep. I can't decide! I'd rather keep both my kidneys, and, anyway, how should I know which one is better?! I know, weird analogy. Point is, I have no favorite.