"Actually I enjoyed them all very much!
If I really had to choose one, which isn't very easy, I'd probably go for the last one. The reason is the horrible epilogue.
The whole 'Deathly Hallows' was a massive amount of epicness with a very satisfying ending. I didn't need and want to know what happens in 19 years. I have something called imagination and interpretation. A corny attachment hinders those.