First of all, Diga Altman is an ancient super dark giant, and his previous power was the power of darkness. In the theatrical version, we can see that among those dark giants, Diga Altman is the strongest one. But in ancient times, Diga Altman turned himself into light and became a giant of light for one person. And people have the energy to teach him light. In the last episode, everyone turned into light and became the power for Diga Altman to defeat him.
Dana Altman is also very strong. Like Diga Altman, he has three forms of power. Miracle form, strong form. You can see it on TV, which is even better than Diga Altman. Dana Altman looks particularly strong, because the bird accepted the power of light in flight and became Altman, saving the earth from now on. Finally, he entered the black hole and his whereabouts were unknown. But we can learn from the following story that he became the guardian of time and space.
So overall, Diga Altman is better than Dana Altman.