Best: Christopher Nolan (directed a masterpiece, an origin story that is still a gold standard in the genre and managed to competently end his trilogy), Matthew Vaughn (made two incredible movies out of some obscure, subpar material, and put the X-Men back on the right track) Bryan Singer (responsible for some of the best moments ever put on film in the genre, and some not so great moments as well to be honest), Anthony & Joe Russo (I feel that no other director(s) before got the medium's energy, how much prep-work inventiveness and creativity it requires to put that energy on screen and how it affects the way they direct superhero movies), Joss Whedon (I still think he is more suited for writing, I don't always agree with his choices but he's great with actors, and I think no movie in the genre struck the balance between spontaneity and masterful structure as much as The Avengers did, and given the task at hand it is a significant accomplishment).
Worst: Zack Snyder (butchered Watchmen, botched a halfway competent Superman origin story and turned the World's Finest into a laughing stock, and given the fact that he had apparently complete control over those movies that's adding insult to injury), Mark Steven Johnson (just like Snyder lacks any form of subtlety whatsoever, missed the mark on Daredevil, tried to make a somehow unintentionally funny parody out of Ghost Rider and of course penned the dreadful Elektra).