Here is my ongoing ordering of the Marvel Cinematic Universe Plus. This list mixes the Universes of Marvel Studios and Disney, Sony, and Fox (and anywhere else characters from Marvel Comics find themselves in the movies. As of now, I am not including live action TV shows in the list, although the shows on Netflix as well as Agents of SHIELD and Agent Carter could fit in. Some of those episodes correspond to Movies down to the week they aired.
As far as this list is concerned, the MCU+ starts with the release of Iron Man because the previous Spider-Man, X-Men, and Fantastic Four movies are all messes of continuity with everything else and aren't all that great of movies compared to later versions of Marvel movies. There are movies that just aren't good enough or don't fit in to make the list. At one point Amazing Spider-Man 2 was in the MCU+ but my apologies for that movie have run out and it has lost its place.
1. Captain America: First Avenger
World War II Story of Captain America.
2. X-Men First Class
Cold War Story of X-Men set during the Cuban Missile Crisis
3. X-Men Days of Future Past (Rogue Cut to be too specific)
Wolverine goes back in time to the '70's. Doesn't count as the future because he resets the timeline to keep the future he previously knew from ever happening. Wolverine has bone claws
4. X-Men Origins: Wolverine
Wolverine in the late '70's or early '80's. Logan gets a broader origin story. It's not a perfect movie but it has some great aspects to it including the incredible title sequence through decades of western war.
5. X-Men Apocalypse
The young X-men go to see Return of the Jedi in the theater in 1983.
6. Iron Man
The movie that kicked off Marvel studios and exceeded all expectations. It's the first of these movies to come out and the spirit of it runs through the Disney MCU. First movie to bring us up to date set in present time.
7. Iron Man 2
I am sometimes hesitant to include this movie because it has some bad cheesy moments but it does introduce War Machine and Black Widow.
This could be my underdog pick to sneak into the top five and it's the first instance of seeing SHIELD in a more official capacity than brief visits with Tony Stark or a tag at the end of First Avenger
New York City is attacked by aliens and partially destroyed. The Netflix shows deal with the city recovering from the destruction.
10. The Amazing Spider-Man
Spider-Man swings from construction cranes that are being used to reconstruct the city after the New York Incident. Spider-Man gets an origin story that doesn't involve organic webs coming out of his wrists.
11. Iron Man 3
Tony Stark deals with PTSD from the events of Avengers.
12. The Wolverine
Logan goes to Japan and loses his metal claws in the final battle.
13. Thor: The Dark World
Loki assumes Odin's identity at the end of the movie.
14. Captain America: The Winter Soldier
Captain America and friends crash three hovercarriers into the Potomic River.
15. Guardians of the Galaxy
While Star Lord's story starts in the 80's, the story follows him as a grown up.
16. Avengers Age of Ultron
The Avengers create Vision using an Infinity Stone
Ant-Man's origin story shows the quantum universe as an aspect in the MCU.
Final battle mixes Colossus from X-Men and a scrapped aircraft carrier that should be read as one of the crashed helicarriers from Winter Soldier.
19. Captain America: Civil War
Cleanly brings Spider-Man into the MCU. By ignoring The Amazing Spider-Man 2, we keep Peter Parker in high school.
20. Doctor Strange
This movie might be further in the future than other MCU movie releases solely based on the first post-credit tag. Thor speaks with Strange about Loki still being alive and Odin being missing, two facts that are not previously known to Thor in his last appearance during Age of Ultron. We'll have to see where the Time Stone shows up next and if the next Thor film takes place concurrently with Civil War. This movie also introduces the mystical side of the Marvel Universe.
21. Big Hero 6
This is a Marvel property in a Disney Animation that takes place in a future city that seems to be a merger between Tokyo and San Francisco. It's a peaceful future where Super Villains are a known thing but not something that exists in their time. I like to place it in the MCU+ as a look at the world after super heroes have defeated all of the super villains of the world but many of the world's cities have required drastic rebuilding (hence San Fransokyo). It is the return of a super villain into the world that surprises bystanders who are in disbelief that he even exists. It also brings to rise a group of heroes who are a reaction to the villain.