It was a tough call for me between the Deku Butler and Mikau, but I went with Mikau. Here's a guy who's got the weight of the world on his shoulders, with everyone looking to him to save the day and put things right. Darmani was in the same situation, but he was a renowned warrior. Mikau just wanted to play the guitar. It's pretty clear he and Lulu had a romantic relationship and it's likely he was the father of Lulu's children, even though he doesn't admit it and they don't seem to have been an official couple. He strikes me as a flawed character unwilling to accept the responsibilities of fatherhood and leadership in general. But when the eggs are stolen Mikau finally does the right thing and steps up to save them and the rest of the Zora, making it all the more tragic when he dies trying.
Maybe I'm reading too much into the subtext Zora Hall is rife with, but those were the impressions I always got. To lose a child as the Deku Butler did must be horrible. But to know your children need your help and to die knowing you couldn't save them seems to me to be worse.