Scarlette Johansson - Black Widow 9 movies including new Black Widow movie
(Aunt) May Parker - also 9 movies if you count the Toby Maguire and Andrew Garfield spider man movies
you got it..Maria Hill I pick her because she was in many action scenes while Happy was in only 2.
Such as Maria was instrumental in saving Captain America in winter solder, she also saved Nick Fury in the first avengers movie.