Darry tops Dally as far as father figures go. Dally sets a terrible example for Johnny, who is so blinded by his own hero-worship that he can't see all of Dally's many faults. Darry, meanwhile, works hard, sees that Pony does well in school and sets regular curfews for him.
Dallas is not really a good father figure. He is too unstable and violent. It is clear that Darry loves Ponyboy, and looks out for him. Darry can be strict, but he clearly has Ponyboy's best interests at heart. I think Darry is a better father figure.
Dallas is unable to look out for himself and is already too damaged to support Johnny. He cares fiercely for him, but cannot offer anything practical to improve Johnny's life. Darry may be strict with Ponyboy, but he gives him a home, keeps him in school and sets a good example.
I would have to say that Darry's relationship with Ponyboy is way better than Dallas's with Johnny. This is mainly because you want your father figure to be setting an example of how things can go well for you. Dallas is in no way setting a good example for Johnny. He's not influencing him to go in a direction where he can have long term sucess the way Darry is influencing Pony.