At the moment it's a draw between Wolf's Rain and Alfred J. Kwak for me. Both are excellent shows with a lot of character development, interesting and deep characters with whom you can sympathise with, quality animation, beautiful music with both epic score and catchy songs, continuity that is maintained so that even the minor characters have later on an important role in the story which in itself deals with some harsh subjects, there are both happy and sad moments, and the humour is never too much over the top so one can feel the drama and tragedy all around.