Some folks have mentioned Cyril and Dedue, and that surprises me.
I like Cyril. He isn't some overprivileged snot like so many 3H characters. He is an orphan who works hard, learns to read, isn't afraid to speak truth to power, and is a lot more grown up than most of the characters despite his youth. His supports with Manuela and Hilda are some of my favorites in the game. He basically tells Manuela to quit being a co-dependent lush, and calls Hilda out for being a manipulative lazy ass. What a champ.
Dedue is probably my favorite character in the whole game, it's funny to hear people say he's the least liked in his house. He is a gentle giant, extremely loyal, would rather garden or cook than fight, handles the prejudice against him with grace, and his return in part 2 is one of my favorite moments in the game. Dimitri doesn't deserve him. None of us Dedue do.