X-Men: Days of Future Past (2014):
I keep going back and forth on whether this is my favorite X-Men movie, or if First Class is my favorite. I'm still thinking that First Class is my favorite, simply because Michael Fassbender's Magneto is, hands down, my favorite character in all of the X-Men movies, and most of First Class is about him.
Days of Future Past is still an impressive feat, though. I was pessimistic about how this movie was going to turn out, but I was very happy to be proven wrong. I don't think it's a perfect movie, but it knocked it out of the park where it counted. The climax of the movie is one of the most intense I've seen in a comic book movie.
Also, James McAvoy is such an underrated actor. He was amazing in both the X-movies he's been in, but he was especially stellar in Days of Future Past.