I said Id do this ages ago, but only barely got around to doing it recently.
Just feel free to ignore this piece if you dont like the ship. I dont mind the other ships, (and they can have just as many good points and justifications), this is just the one that I like and prefer. So please, no bashing. Id hate to have to remove comments or turn them off completely.
These two are quite possibly my favorite ship out of any fandom. ^^
They both start out so innocent and naïve - just these uncertain little kids who grow up so much throughout the story - into capable, strong, independent teenagers. The animators were absolutely brilliant in portraying that, as well; the changes are slightly subtle, but you can definitely tell that the characters have aged a lot at the end, compared to where they were at the beginning of the series.
Its interesting to see how their relationship grows throughout the story, as well. I love that Mike and Bryan, and the writers, were able to create such believable, complex characters that are capable of change and deep thoughts, making incredibly difficult decisions, holding true to their beliefs amidst the adversity and problems around them, and having the will to admit that they have weaknesses.
Aang has just about one of the sweetest, silliest personalities, and always looks at the bright side of life, despite all of the difficulties hes been through - the genocide of his people, especially. Although he can occasionally be irresponsible, hell take the role of leader when its most needed. He has an incredibly genuine, caring heart, and has been one of the most forgiving characters of the series.
Katara is very strong and isnt afraid to stand up and fight for who she is. She never gives into despair - always believing that there is some form of hope - no matter how small. Shes very protective, as well - watching out for the group, listening and offering advice. Her brother, Sokka, even admits that he really relied on Kataras strength - and that she was what kept their family together after their mothers death.
I just really love the dynamic of the two - Kataras always there to listen to Aang, bringing him away from whatever pain or sadness hes going through - and reminding him that theres still good and hope in the world, while Aang encourages her through her fears and vulnerabilities, and reminds her to smile and see the happier things in life.
I find it very true, sweet, and adorable.
Whew, bit of a long post.