First, Wonder Woman.
In regards to content, I found the first third of the movie on Themyscira (the secret Amazon island) to be the most interesting. Production-wise, Patty Jenkins (the director) avoids making the star's attractiveness the center of the film, a temptation to which other directors might certainly have succumbed. Though the plot has some holes in it and the climactic action seen was CGI-cluttered, it was good to see a powerful, world-shaking female character in a superhero film. That is something sadly lacking.
There are have been a number of reviews of Wonder Woman from this kind of feminist angle, such as this very insightful piece by Zoe Williams. As I watched the Supergirl television show, I found it also attempting to strike some of the same chords. (To be honest, the show is not very good. What I've seen hasn't been terrible, but it's also quite soap-opera-ish, if that's a word. Fair warning!) The pilot episode finds Kara Zor-El (Kal-El, or "Superman's" cousin) having chosen to hide her powers so as not to attract attention. She's initially happy to stay in her male cousin's shadow. The resistance she first gets from friends and family when events draw her out into the superheroine role could speak to the pressures in society for women to stay quiet, not rock the boat, and defer to men. Otherwise, there are several playful debates on her title: why is it Supergirl and not Superwoman?
One of the best episodes I've seen, though, shows Kara battling the android Red Tornado and having difficulty overcoming it because she's afraid to get angry. This leads to a fascinating conversation between Kara and a mentor about the costs involved when women show anger in the workplace: for men, it's seen as assertiveness, while for women, it's seen as threatening and disruptive. Kara needs to overcome that socialization. From the picture below, I'll let you decide if she succeeded.
My favorite feminist superhero has to be Buffy, though.
While the Wonder Woman character and movie has traditionally drawn on Greek mythology, I always saw powerful currents of Hindu goddess figures in Buffy's role as slayer "(i.e., "death-bringer") to demonic forces. In Hindu mythology, the goddesses Durga and Kali come into existence for the express purpose of purging the earth of evil figures. In some cases, the iconography is uncannily similar. Here for instance is a popular devotional image of Kali in her role as destroyer:
Compare to Buffy, at her most merciless: