What I find neat about Atla is that you can put any of the kids into the Avatar role and it's still a fun and interesting story.
Zuko is a classic one for that. Bro was send out to capture the Avatar and turns out he is the Avatar?? You mean to tell me that the Fire Nation could have had the literal Avatar on their side and won the war because Zuko was literally so damn loyal and desperate for his father's approval and Ozai fucked it up???That's beautiful.
Zuko returns to fight his dad only to find that- Hm. Father, did you do something to your hair...? Or is it because I've been away for so long? It looks... Uh... Really thin? And shitty? Ozai shoots lighting at him. (it has not always been that way. Ozai has been ripping his hair out in frustration since he found out that Zuko is the Avatar)
Katara being the Avatar is also great because she just fits so well in that role. She really wants to help people and stop the war. Also, Sokka would have an aneurism when he finds out his sister is not only a waterbender but also an everything bender. He isn't safe from any element anymore, the annoying little sister will always get him.
Speaking about Sokka, he is another hilarious candidate. Sokka being the Avatar? "Magic water" Sokka? "Spirit mombojombo" (I do not care if I spelled it heinous wrong. I refuse to look it up. It what Sokka would have wanted) Sokka? "I don't belive in any of that shit" Sokka? Being the Avatar? 10/10, no notes.
Toph being the Avatar would be fucking terrifying. The show would only have one season and most of the time it's the gaang trying to stop her from committing murder while she learns to see with every bending style possible. Imagine a Toph who could feel the vibrations in the air.
God have mercy for she won't.
Suki is fun to me because I imagine her being really nonchalant about it. She's still a Kyoshi fan girl but for her being the Avatar is just... there. She prefers to fight like a Kyoshi Warrior. The gaang doesn't even find out that she's the Avatar until she uses earthbending to create the border for a campfire, uses airbending to gather and dispose some sticks into it, lights it with firebending and uses waterbending to fill up the pot to make some soup or something.
Is it possible? Maybe not, but it's funny to me so I don't care.
Azula being the Avatar is really interesting to me because while you could make her an even stronger antagonist or something, I like a different idea more. I think it would be interesting if she gets her breakdown earlier and runs away because- well, she's the Avatar! The enemy of the Fire Nation! But she can't be because she is Azula! She is the perfect princess and firebender and loyal- well, loyalty didn't safe Zuzu from being burned and banished- but he was a fool! And she isn't a fool! But she is the Avatar...
I feel like Mai would be similar to Suki. Just because I think it would be funny.
Like, imagine she throws a knife at you but then you see her be too lazy to go pick it up so she just uses airbending or earthbending to get it back just to stab you with it.
Ty Lee would just use it to gaslight people. What? Bending?? What are you talking about? She's an acrobat. Have you seen her in the circus? She's great! Airbending? Wow, way to dismiss all the hard work she put into her skills! Shame on you.
Jet (and the other freedom fighters in a way) would be neat too. Like, being the Avatar would also make him a firebender. And he can't be a firebender. They're monsters, they are horrible. He won't use it. He won't.
Yue being the Avatar is also interesting. Mostly because of the political reasons. And because I'm stupid I won't get too deep into it but I'm sure you get the point.
Although it would be fun to have someone be the Avatar and the moon spirit. Maybe that would have to be changed idk.