Changes every season! Lol here:
Momo, for reals. Sokka for humor, Zuko because he's a good person on the inside, and THE SINGING NOMADS. Oh yes.
Probably Zuko, hes a character who overcomes his past and internal conflict and I really like the parallels with Aang, especially in Episode 1 of Book 3 if I remember correctly. Iro is great, Toph is awesome, Aang is ok, in my opinion he got kind of annoying in Book 3. Sokka is funny. Suki is awesome because of the parkour in the Boiling Rock episodes lol
Tie between the Cabbage man, Momo, Sokka, Toph, Bumi, and the hippie dude with the ukulele. :) I really liked them all though...
Sokka and Iroh are my favorites. But I have to say Zuko and Aang are most interesting.
Toph all the way. Along with Zuko and Iroh.