Any kind of growth in general is my favorite, but I like it most when the subject starts out small and just becomes huge in general. I definitely have an ass preference, though.
Best part of making this game is the images because I'm the only one who gets to see any bonus content 😈
Besides, I've never actually programmed a game and it's proven to be a painful process. I also don't like writing which makes a story driven game kind of hard.