Quick! What's your favorite...
Tales of Ba Sing Se, might be another episode, been a few years since I've seen the show.
JL and JLU are probably the best we'll ever see with regards to a show with an episodic nature that really nicely crafts an overarching story in the background.
I think Last Airbender is a better overall story telling experience.
All of season 3
Republic City was independent of the Earth Nation and Omashu had it's own king. Plus Zaofu was stated to be independent of the Earth Kingdom multiple times. City-States definitely count.
Zuko Alone or the North Pole Arc, the Drill is definitely up there too. The whole fucking series.
Zuko, Sokka's cool too, and so was Toph and Iroh and the whole fucking cast.
This one's easy, Earth.
Air. Borderline telekinesis and retarded overpowered.
Sokka is best character. In a world of gods, he is a mortal on the same footing as them.
He also gets all the bitchs.