So, I commented on a post in
katara_zuko, intending to keep it short and simple, but I... kinda went into a huge, essay-like rant. ^.^;;
I'm kinda happy with ho it turned out, so I figured I'd post it here for safekeeping.
I think they're better for each other because of evidence form the show.
Aang clings to Katara. She's the first girl he sees after a hundred years frozen in an iceberg, the first girl he ever crushes on, and he clings to her, begging for praise and attention. And because he wants her to like him back so badly, he's willing to sacrifice his duty to the entire world just to be with her - something that is not good, since accepting his responsibilities would be a huge step in growing up.
Katara, on the other hand, is caring and protective and all around motherly. She tells him she's proud, helps him when he's sick, and goes out of her way to make sure he has what he needs to be healthy and happy and able to do what it takes to save the world. She gives and gives and gives, and he just takes. On top of that, as I've mentioned before, she has to restrain herself around him - he has clearly shown that he can't handle her quick temper or the way she snaps at people. Not when it's directed at him, anyway. She's known Aang since the moment he was hatched from the iceberg, and seems to feel a certain amount of responsibility because of it.
There's no real balance with them. They don't push each other to do well - Katara is too soft and motherly towards Aang to give him the shoves he often needs in order to man-up and do what he has to. Aang drools over Katara and does things so she'll like him, not so she has what she needs or is happy. And if he is protecting her, he usually goes into a violent rage that she has to pull him out of. And everything Aang does around her seems immature and childish - by season 3, forcing himself on her seemed rather common place, even going so far as to kiss her when she said she was confused and needed space. That's not healthy for either of them.
Then, with Maiko, Zuko is someone who likes to talk about his thoughts and feeling and actually have someone listen. That's what his uncle always did for him. He needs someone who will listen and sympathize, but who will always push at him to follow his own heart, to not worry about pleasing the world around him and to stop doing what people tell him to, and to keep his temper in check. Again, Iroh provided a bit of that support, though he was very subtle with it.
Mai, on the other hand, just wants someone to be with. She doesn't care about talking or listening or anything complicated - she just wants the pleasure of spending time with her boyfriend. And there's nothing wrong with that. But what she needs is someone who will encourage her to express herself and break free from the emotionless facade her parents forced her to adopt, someone who will be patient enough to help her break a lifelong habit.
Mai and Zuko like each other. That's obvious. But it doesn't mean they work. Mai can't provide the understanding ear or forceful attitude Zuko needs and wants, and Zuko can't be the calm, patient person who helps her work through her own problems. They get along and enjoy each others company, but they don't build off each other at all - in fact, they seem to push one another back.
Zuko and Katara, on the other hand, have already proved within the series that they work well together. Katara can be patient and understand, as well as forceful and stubborn - exactly what Zuko needs. Zuko, on the other hand, can more than handle her temperamental outbursts (and probably calm them, too, either by countering with his won temper or reasoning against her pointless anger) and would be perfectly willing to give her a shoulder to lean on. And Katara wouldn't be afraid to yell at him - they started off as enemies, so she doesn't feel that same level of maternal-ness or responsibility. On the same end, Zuko wouldn't worry about how Katara responded to his thoughts - she listened in Ba Sing Se, when they were still bitter enemies, so why stop when they're friends (or more)?
And Aang works well with Toph. Toph is pushy and stubborn, so she'll never let him get away with same things Katara did. She would know when he's facing a serious issue and needs comforting, and when he's just being a whiny baby who doesn't want to deal with the tasks set in front of him. And Aang would be good for her, too. His flexible personality would help combat her stubbornness, and he could probably teach her to approach things from different views, like an airbender instead of an earthbender.
Mai? Mai would do well with Ty Lee. Not necessarily in a romantic sense (though I wouldn't complain), but just being together. Ty Lee is the epitome of free-spirit and self-expression, someone who never hesitates in letting loose and showing people her true feelings. Mai could learn and grow from that, and hopefully break free from her controlled, emotionless state.
They all just... work. They complement each other, bonding on their similarities and building off their differences. That, to me, is a very healthy relationship.