I'll throw my two cents too:
1- X2: I mean come on (although it should be the worst because the final seconds of that movie made us the biggest cinematic promise that was never fulfilled).
2 - X-Men: You think the frog line was bad? Well the rest of the dialogue is amazing, just a quick example of character interaction and exposition beautifully combined:
Xavier: “You don't like him, do you?”
Scott: "How can you tell?”
Xavier: “Well, I'm psychic, you know.”
3 - X-Men: Days of Future Past (Theatrical or Rogue Cut, pick one): The return of the X-Men in true form, an amazing score, the perfect ending, the true final X-Men movie.
4 - Deadpool: The movie that took all of the great undertones of the X-Men lore, made fun of it, and also took it more seriously than most of the others.
5 - Deadpool 2: Not as funny as the first one, and some weird turns in the second act.
6 -Logan: I had a really big problem with the last act, but mostly cause I tend to hate kids in these types of movies, and the overabundance of them in the last fight was just unforgivable for me. It's still an awesome movie.
7 - X-Men Apocalypse: What? that movie was terrible! Was it really? The opening Egypt sequence alone elevates this movie to incredible heights.
8 - X-Men: First Class: I had big expectations for this movie, and I know a lot of people loved it, I was sadly not one of them, just the codename picking scene to this day bothers me so much, and other stuff that I won't get into now, but I can say without a doubt in my mind that Magneto has never been cooler than in the first act of this movie.
9: X-Men: The Last stand: This is a bad movie, but you know what?, this is the last movie that had all the original cast, and guess what? they were amazing saying those stupid lines, and wearing those stupid costumes. John Powell did an amazingly moving score for this one, that Ratner managed to almost destroy in the final mix in the movie.
10 - The Wolverine: This movie is better than TLS, but still if I had to pick between watching this one or Last Stand on cable on an afternoon when I'm sick in bed, I'd rather watch the other one, also talk about a self imploding third act.
11 - TIE Dark Phoenix & X-Men Origins: Wolverine: Yay we did it! end of the list.