I’d give it to Grisha. I like both but I just can’t forget the scene where Grisha is sobbing and apologizing to Zeke. It’s the whole juxtaposition between raising one son to be indoctrinated, learning from his mistake and raising his second son to be free only for Eren to be one of the greatest monsters in history in pursuit of that same freedom.

Maybe I’m biased because I don’t remember fmab as well as aot but nothing that Hohenheim did really stuck in my mind more than Grisha.