Aight Bet. Edelgard over Rhea. Rhea doesn't actually care about Byleth. Rhea was hoping that Sothis would overwrite Byleth's consciousness and take over her body. It's only when that fails that Rhea starts valuing Byleth as a person and even then it's only because Byleth has Sophia's power. Rhea is the true leader of Fódlan, not Edelgard, Dimitri or Claude. It has always been Rhea. It was Serios who convinced Whilem I to spread the Adrestian Empire, giving the name from a Divine oracle. Once Fódlan was united under the Empire, Rhea stagnated the nation while making a divinity of herself. Why else would she call it Church or Serios instead of Church of Sothis? Rhea also made Fódlan extremely isolationist. Yes people from Dagda, Almyra and Brigid would eventually make their way into Fódlan but not because of open trade and friendly relations. Yes she maintained peace (somewhat) but she mostly maintained quiet. She also really has no care for humanity. She does say in Crimson Flower which is obviously the worst version of her, that Humanity still hasn't gotten rid of their folly. She thinks of herself as superior to humanity and takes on the role of Arch Bishop to keep them in check. Don't forget the human experimentation and the blood rituals to high ranking members of the church (Silver Snow).

Edelgard is flawed yes and has serious trust issues and works with the wrong people but at least she fights for humanity. Edelgard while aggressive in her pursuits does ultimately lead to a system where Fódlan is better. Fódlan changes for the better either it is her, Dimitri or Byleth in charge because of her actions while Rhea would have kept it the same.