This is a very nice question, thank you! For favourite I'd say probably Lottie. She doesn't get a lot of screen time but I really love her as a character and I like to imagine her little shenanigans at the castle. I'm also very fond of a character we made up: Noel. He is one of Vincent's cadets and I kiss his forehead everyday (I'd like to say more but he'll be a plot point later on, so just know he's a good boy). Oswald, Lacie and Lottie interacting are the funniest to write lol. For single character I'd say probably Leo. Elliot is the easiest alongside Gilbert! (You didn't ask but the most difficult to write are Levi and Jack afhofegfe)