It depends on what time period you’re talking about (energy-bending notwithstanding). Give her some time to improve her technique–what, less than a decade she could come out on top in a fight.
Presently? Ozai is straight up the most powerful firebender in the world; the only person capable of defeating him in a straight fight is Aang (even Iroh, who used to be the more powerful of the two, backed this up). This is pretty justifiable, considering he spent a lifetime training to get where he is and–unlike his brother–hasn’t fallen into any kind of physical decline that would through off any results. Azula may be a prodigy, but she’s still very young and hasn’t developed or mastered some of the techniques her father has.
His fire may not be as hot scientifically (I see Ozai’s fire as being more about concussive, explosive force than heat), but he has a stupidly high amount of energy to burn, considering how sustained and consistent Ozai’s fire bursts are, and his flame jets are more developed. Azula’s lightning conjuration is a little slower comparatively and not as smooth. Ozai is also known to form lightning with both hands at once; does that make it stronger? Who knows, but it is impressive-looking.
While Azula is a master in her own right, she’s kind of like an apprentice to her father–especially since he did teach her somewhat. Will she surpass him in the future? Yes. Has she yet? No.
MD: Zuko’s conflict with his siter came to a head during the finale, when they fought each other in an almost-deadly Agni Kai. This emotionally charged duel was the highlight of the finale for us. Azula vs. Zuko key animation by Jung Hye Young and Yu Jae Myung. Designs by Angela Song Mueller.