While things have happened that made the gAang not be too fond of Zuko, I still see him as the most likely candidate to stand with them when they fight Fire Lord Ozai. If there was the option to have Zuko and Iroh, I would have chosen that instead.

There is a chance for Azula to betray Ozai as a bid to get the throne, but I don't think it's really that large. All things considered, Azula is sitting in a very good spot to be the next Fire Lord/Lady. There's zero chance her 'failure' of a brother will have his birthright restored, even after helping her conquer Ba Sing Se. Odds are, Zuko's achievement will be played down by Azula. At best, Zuko will be allowed back to the Fire Nation as a 'war hero,' but he won't have his birthright. Ozai is a second child, and favoring his second child is very obvious. Why would Azula want to betray him? Just to get the throne earlier? In the spirit of her father, Azula may plot and plan his demise, but she would use others to achieve this end, manipulating the circumstances (even with the use of the gAang perhaps?) so that the Fire Nation's only option is to have her succeed her father. The thing is, Azula is only fourteen and this good at working the situation to her advantage. I can't imagine how good Ozai must be. So, it really depends on whether we'll see a greedy side of Azula that doesn't want to wait until adulthood to take the throne from her father, or if she'll just be content to take over the rest of the world, safe in the knowledge that stupid Zuzu will never get the throne.

What would be awesome would be an 'Avengers Assemble' sort of thing for the gAang when facing against Ozai. Bring out all the most helpful characters! King Bumi, the Mechanist and his helpful inventions, the Kyoshi Warriors (whatever's left of them), and the Freedom Fighters (such as they might be)! Battle royale for the fate of the world! Aang must rely on the power of his friends to see him through this, so why not bring out all his friends to help him succeed?

I'm still seeing Zuko as more likely, especially with all that change-of-heart stuff at the end of Season 2. Given Azula's temprement, i feel it likely that she'll double-cross him, or Ozai will double-cross him, or Zuko will go mad, or... well, I dunno. But i doubt ZuZu will stick with his insane sister.

i think iroh, because near the end of season two, he started to show high dislike of his brother. zuko might not happen due to the fact he is so cought up with his honor, and azula, tye lee, and mai are fire nation all the way. he earth king as we know so far has no bending power, and bumi is still in new ozai. the people at the air temple are to far away, and probly have to deal with the flying ballon thing. we dont know what happened to jet and them, so for the sake of this, lets leave them out.

I was thinking of checking if there was a thread already made for Zuko's intentions and ambitions, and if not making one, but I'll put some of it here.

I think that Zuko will be the one to side with Aang in the end. My prediction for Zuko is that he realizes now that his real family, Ozai and Azula, care nothing for him, while Iroh truly does. I believe he sided with Azula only to get a foot back in the door of the Fire Nation either to overthrow his father eventually, or at least beat Azula out for the position. Of course, he can't outshine Azula as he is now. So he'll train hard.

At the end, I feel he'll side with Team Avatar and help defeat his father.

At least that's my opinion, or as much of the Zuko theories I'll put here.