I don't really have favorites, but I liked a lot of anime I watched.
For this, I'm choosing K-On!.
K-On! was honestly my favorite anime. Fun characters and dialogue, music, drums, and a really good ending.
It's what got me into anime. What started the whole craze.
So, K-On! took the spot
(also, pictures of faucets during songs)
(and cat-ears)