Speaking purely in terms of visual design, the female characters I like include Fremy from "Rokka: Braves of the Six Flowers." Her all-black, unadorned outfit makes her white hair and the flower on her head particularly striking.

Also Riyo from "GACHIAKUTA" - actually, all the characters in that work are extremely cool. The author is very talented at character design.

I also really love Yoko from "Gurren Lagann."

Vi from "Arcane".

Selesia from "Re:CREATORS"

Yeah, I absolutely love sexy red-haired girls. 