So, considering this is a zutara board, everyone reading this will probably ship zutara, but I wanted to write this anyway. I don't know anyone else who ships zutara, so I thought this would be a good place to say exactly why I love zutara so much, and why I don't think kataang would work out.
First off, I'd like to point out, I loved kataang when I first watched the show. Granted, I was about 5 years old, but I'm still not completely biased. I rewatched it again this year, and in season 1, despite knowing abut zutara, I liked Kataang. It was cute, and it was obvious Aang liked Katara. They felt very close to eachother, and they both blushed at least once for eachother. The first "zutara" moment, where Zuko tied katara up to the tree, felt uncomfortable and creepy to me, and I leant even more to kataang. Despite all this, I actually didn't ship kataang. It lacked substance, and a spark, but I assumed that would be built up in the following seasons.
Spoiler alert: It wasn't.
So now we're at season 2...ahhh, season 2, where we meet toph, Azula, swamp people and my first zutara moment. Happy memories. Although season two was a great season, kataang kind of went down for me, and not just because of that crystal catacombes scene (which I'll talk about later). I can't actually think of a single time Katara blushed for Aang in S2, despite his crush in her was just growing and growing. Nothing in their relashipship was built up, and it made me feel like Katara got over whatever bit of her liked Aang (ie one blush). Sure, maybe she kissed him in the cheek once or twice, but I feel like that was more just making him happy. It seemed like the creators kind of forgot about kataang, and then at the end, tried to push something by adding in that "I can't let go of Katara! I love her!" Bit with Aang and the guru. It's funny how kataangers think Aang saying he loves Katara makes kataang the perfect ship, because it doesn't. It's like if I said I love calum hood, that's doesn't mean we're the perfect match and you should go off shipping bralum or whatever our ship name would be. Sure, you can say Katara loves Aang, and I have no doubt she does, but not in the way Aang loves her. Katara loves Aang in an almost, if not completely, motherly way. Aang, on the other hand, fantasies about kissing her. Aang feels an attachment to Katara, that he feels he can't let go of. The thing is, if Aang really loves Katara in the way that a relationship should be built off of, he should be happy if she's happy. What would make Katara happy? Putting a stop to the war. But instead, Aang thinks about his feelings for her. The same happens when he unlocks avatar state and he says "I'm sorry Katara." For what? For making her happy by unlocking the power to put an end to this war? No; he's sorry because he thinks that letting go of her will cause them not to have a romantic relationship, and he thinks that if he wants a romantic relationship with her, she obviously does with him. He's actually sorry for himself.
Now, the scene that turned me into a zutarian: the crystal catacombes. Even though I didn't think much of the part where Katara's yelling at Zuko when I was watching it, looking back, it just adds to the scenes. You can see Katara hates Zuko. She hates him so much that she's even made assumptions about him ("you're the fire lords son, spreading war and hatred is in your blood"). Now, seeing Zuko's past with his family, I would be hurt, and probably super angry at the comments she's making. But what does Zuko do? He just listens. He lets her rant. Because he knows she has every reason to hate him. He knows he's done wrong in the past. And he feels bad. When he says "that's smething we have in common," I take it as his own little way of comfort. They may be from totally different life styles, and opposite sides, but he still gets her. He understands what she's talking about. Then the next bit that's shown with them, she's apologising. Katara's apologising to the guy she was full-on shouting at...maybe half an hour ago? That is the effect he just had on her. Then the fact that after such a short time of beginning to trust him, she actually offers to use the spirit water on him. A lot of kataangers say it's just her motherly instinct, but Katara has never shown any motherlyness to Zuko (which I'll bring up later). Then Aang and Iroh break in, Zuko and Katara move closer (!!!), and Aang gives Zuko that death glare. Oh, that pissed me off. Is Katara your's, Aang? Are you going to give eyebrow threats to every guy who gets near to her? I realise he likes Katara, but she was the one who offered to heal Zuko's scar in the first place. I mean, if Zuko was doing anything wrong, Katara would have waterbended his face off or something. And then when Katara leaves, and she just looks at Zuko, half-hopeful, and he just looks away. What does that remind me of? Oh yeah, that reminds me of ANY POWERFUL ROMANTIC RELATIONSHIP WITH SUBSTANCE THAT IS USUALLY IN AN EPIC LOVE ROMANCE NOVELS AND BECOME BESTSELLERS!! sorry, I got a bit enthusiastic lol.
Then in season 3, zutara goes wayyyyy up and kataang goes wayyyyy down. Now, I know there was that dance between Aang and Katara, which most kataangers found hot, but Katara probably just thought was a bit of fun. I personally just saw some kids dancing around and having a good time. Another thing is Aang's ignorance of Katara's feelings; when he forces the kiss on her, he doesn't even apologise, he just knows he did something wrong because she runs away. When Zuko joined the gaang, and my hopes of zutara were resparked. At first, Katara hates Zuko, and it's understandable; he betrayed her. The others are willing to trust him, but she isn't, because what happened in the crossroads of destiny ep was personal. Now, as far as we know, she's only been betrayed by one person before, and that was jet. He showed up, all charismatic and heroic and impressive, so it came as a huge shock when he betrayed her. Even so, she was still willing to trust him when they meet again. With Zuko, he's been the enemy to her for the whole time, just like he has been with Sokka and Aang. She began to trust him, and he betrayed her, but would it have come as a big of a shock to her as jet? Probably not. Yet, for so long, she absolutely refuses to trust him again, because she thinks he'll betray her again. But this also shows again how much their little conversation meant to her, and, romantic or non-romantic, there were strong feelings between them.
When Zuko says he can help her find her mother's killer, the look in her face says it all. When her mom died, she didn't have any time to grieve, she was immediately given a bigger, adult pair of shoes to fill. For someone to actually think of her, and only her, especially with a topic like her mother's killer...it must have been unreal. We've never really seen Katara as a dark character, but in TSR, we do. She even uses bloodbending, as her own choice, to the man she thought had killed her mother. We see Katara at her lowest, darkest point in this episode, and guess who else sees it? The only other person in the gaang who sees it? Zuko. At the same time, we can see that even though this mission was for Katara, it's personal to Zuko too. When he tells Yon Rha to look at Katara's eyes, the way he says it shows that 1, he cares about Katara and 2, he can connect with this mission. He feels the need to do this, because if he was in Katara's place, he knows what he would do. On the other hand, Aang in TSR, shows exactly why I love zutara: they have empathy that kataang will never have. I'm not saying that it's Aang's fault that his losses are different than his, but it's the way he tells her how she should handle it, without properly understanding what she's going through. He was brought up as a peaceful little monk, he doesn't want to get revenge or justice. But Katara's darker than him. She want to get revenge, and it's Zuko who understands what she's feeling. Aang doesn't have the right to tell her what she should do, because he doesn't get it. It'd also that he said forgiveness is the first step to healing, because it's not; closure is, and Katara never got closure. And you can see, she didn't forgive Yon Rha, but the trip obviously affected her and helped her begun healing.
When Zuko needs to decide who to bring with to fight Azula, he chooses Katara with about half a second of thinking. He knows they work as a good team. When he takes the Lightning bold for her...he said one single word, and it's filled with so much raw emotion, and the same when Katara yells out Zuko's name. When Zuko jumped for that lightning, he knew he wasn't going to be able to redirect it. But he jusmped anyway. You can see Katara isn't thinking too clearly when she's up against Azula, and the relief in her eyes when she heals Zuko is amazing. This is how Katara spends the finally: arguing with Aang, being in battle with Zuko, where he takes a bullet for her, and every single emotion is at it's peak, then kissing Aang. Because that makes sense.
Another thing is that Aang is s child. Now, I know, the age difference with Kataang and Zutara are both two years, but we see Aang as a kid. Sure, he faces his responsibilities and saves the world, but at heart, he's still a child. Katara, on the other hand, is an adult. She may be 14, but she grew up too fast, and viewers see her as an adult. I was arguing with a kataanger once and I told them this point. They replied with something about how Katara is selfish in a childish way, but they didn't really get he point. Every adult is childish in one way or another, but that does not make them a child, or give them a mindset that matches a child. With Zuko, he grew up too fast as well, and we definitely see him as an adult.
As I said before, zutara has empathy. Some kataangers mock that Zuko and Katara can share "mommy problems", and to be honest, they can, but it goes deeper than that. A big part of relationships is understanding, and zutara has that. Zuko and Katara began understanding eachother when they were locked in a cave together for one hour at the most. With kataang, I see very little understanding, and I'm not even thinking about empathy right now, I mean basic understanding of eachother's feelings. Also, zutara has great understanding overall, but family problems is a main one. The thing is, you can see how much the loss of their mothers affected both of them and shaped them as people. With Katara, it made her grow up to fast, taking on adult shoes when she should have been taking on preteen ones. You can see how deeply and strongly she feels about her mother's death, and how much she truly cares about what happened. With Zuko, his circumstances were different, but his mom leaving really was a game-changer for his life. It hardened him as a person, and it took away that protection and love that he only got from his mother. Katara and Zuko understand this about eachother so easily, and their relationship was influenced by that.
Also, Katara is motherly to Aang, it's a canon fact (seen in the runaway). Katar is motherly to nearly everyone, it's just in her nature, but they don't put Katara and Toph in a romantic light, so it's fine. As a said before, Katara's live for Aang is motherly, and while that's a very powerful love, it's not romantic. The only people we see Katara not mothering are guys she likes (like jet). Katara doesn't mother Zuko. Even when she cares for him, you can see it's not in any way motherly. If it was, Zuko wouldn't accept it, because he doesn't want motherly love from anyone but his mother (*sob*). Honestly, even if Katara did have more prominent romantic feelings for Aang, I don't think Kataang would've worked out. Every character has a flaw, but Aang's, being selfish and Katara's, caring too much, would've clashed. They want different things in a relationship; Aang wants freedom and fun, Katara want something meaningful and emotional. Aang would be bored, Katara would be frustrated. On the other hand, Zutara is so interesting. Katara and Zuko are conventional opposites; water and fire, ying and yang, hot and cold, etc, but at the same time, they're similar; they are both highly emotionally orientated people who aren't afraid to speak their minds. Katara cares and is persistent enough to get through Zuko's confused or angry patches, and he is calm enough around her to get through her crazed freak outs.
In the end, zutara has understanding, empathy, similarities, awesome opposites, comparisons and accidental dressing up as spirit lovers, and Kataang has blushes and a one sided crush. This, ladies and gentlemen, is why Zutara will always be my OTP.