Supergirl's red and blue costume has become a popular one. The red cape paired with matching short skirt looks great.
Marvel character, Scarlett Witch has also emerged as one of the most popular character with it's costume being a favorite of many.
Captain Marvel might have been a hated charfacter in Avenger movies, but her costume definitely is one of the best designed.
While Black Widow doesn't have any inhuman super powers, her costume with high tech gadgets is pretty popular among fans.
Ekektra movie came out way before Marvel build an empire on superheroes. The character's red costume became instant favorite among fans.
First Lynda Carter and then Gal Gadot made Wonder Woman's character along with it's skimpy costume popular among fans. The shield, sword and lasso looks perfect.