my favorite chacaters have to be iroh and zuko, believe them to be some of the most well writen of the lot. while zuko has better charactr development, there is such depth in iroh form the start of season one. he may seems like a dopy old fool, but inside he hides great sorrow, wisdom and strength. episode 35 made me like him so much more, when he made me cry while signing to the memory of his dead son while crying himself. he may bot say this, but i think it would be in his personality to say something similar "to know great joy you much also know great sorrow. after the worst day in your life, your able to cherish the smallest of wonders in the world." i believe that sort of his philosophy.
out of the main 4 i like tph the best. and momo. and of the old masters (apart from iroh) boomie is my favorite, he is also my favorite comdey relief character, with sokka as a close second.