Female Nohr: Camilla (surprise, surprise).
Her hair is lovely, she has a nice figure (tall and curvy), her crown is really cute, and her armor is pretty cool looking. I actually think that the "battle panties" look neat on her due to the fact that she has armor and cloth on her hips and thighs. It really manages to pull the outfit together.
The runner up would be Elise. She looks like an adorable gothic lolita.
Male Nohr: Leo. I love the black armor that the Nohr siblings all wear very much, and I think that Leo manages to wear it the best. I'm also a big fan of his hairstyle.
Inigo still looks great in this game too (he was my favorite male design for Awakening).
Female Hoshido: Hmm, I suppose I would pick Hana because I'm a big fan of her outfit (I think her face is a bit too plain looking though).
Selkie also has a nice design.
Male Hoshido: None. I'm just not a big fan of any of the male characters in terms of design for Hoshido. :/
They all either look kind of plain or have certain things that I hate about their design.
None of the all path characters impress me much in terms of design (as much as I like Jakob).