I voted Monster Girl because that's what I feel like has biggest gap between popularity and its current representation here (mind you, I'm ignoring all the genres of things that are reprehensible like underage or incest).
But I'd love to see more Yuri, dark skin, chubby, and muscles (specifically buff chicks). I'm also assuming Monster girl covers some other stuff I like but I'm pretty sure it doesn't (strange creatures like aliens or furry/scalie stuff or orcs/trolls/what-have-you).