As well as Mako.

Believe it or not I do have Iroh and Azula switched. Though I love Azula much more, I think that Iroh has experience on her.

He`s definitely up there

I agree with everything Zuko and below, but for the top three I have 1) Iroh 2) Ozai 3) Azula

She has accomplished more at a young age than Iroh has in his current age. What took him studying of waterbenders to learn how to redirect lightning, she managed to learn on her own without anyone to teach her. She can both generate lightning and learned the one skill that she didn't know on her own in such a short time that took Iroh and Zuko much longer to learn. She possesses fire that is not only a different color and hotter than normal fire, but is also a skill that no other firebender that has been seen so far has had. The only other creatures that have this power as well that we've seen are the two dragons. Her power is so great that it is comparable to freaking dragons, which is the source of firebending to begin with. She took down her teacher that had more experience than her without much effort when she was just a child, as revealed in the comic The Search. She can even still maintain her amazing powers when she has lost her mind. I'm not just saying this just because she's my favorite character but because I genuinely believe it. Iroh may be more experienced but she has proven to have accomplished more with her level of power as a young age than he has in his old age.

^agree with this, the question is who has the most power, not who is the most skilled. I think Iroh would beat her in a fight, but only due to his incredible skill and experience and Azula's temperament and emotional instability.