Ozai. By a mile.

lao did not burn the children's faces, did not beat them with lightning, did not expel them in order to catch the avatar. so he's worse.

Lao was just an overproduce parent, who was concern with his daughter well-being due to her blindness. He did not trust Toph to take care of herself until the comics where he started to respect her as a person and her way of life.

Lao was overprotective but for a good reason, he had a small blind daughter who he thought was completely helpless(She contributed to this by playing the part) then when he found out what kind of danger she constantly put herself into he became even more so. when reuniting with her, in order to cope he disowned her but the two reconciled and had a pretty good relationship going forward.

Ozai tried to kill his child the moment he was born, abused him for thirteen years emotionally and physically. told him to his face he wanted to kill him and that he was lucky to be born. agreed to kill him AGAIN. fought him for trying to protect the innocent and publicly mutilated him in front of hundreds of people. banished him for refusing to fight. then tried to kill him AGAIN after zuko told him off. Ozai is literally the worst father in the atla verse, the only person who gets close is yakone.

Hmmm, overprotective because your daughter’s blind vs burning your son’s face, choosing exactly where an eye is. I wonder who’s the worse father?