Granted it's been years since I've seen most of these, but that's mostly because they weren't that great the first time around.
1. Avengers 2. Guardians 2 3. Iron Man 4.Thor-Ragnarok 5. Ant Man 6. Avengers-Infinity War(hard to buy in fully when you know the "emotional" ending will be undone, otherwise would be much higher) 7. Guardians of the Galaxy 8. Black Panther 9. Capt. America-Civil War 10. Capt America-Winter Soldier 11. Dr. Strange 12. Ant Man and the Wasp 13. Capt. America-First Avenger(might have to move this one up) 14. Spiderman-Homecoming 15. Avengers-Ultron(I like listening to James Spader pontificate) 16. Iron Man 3 17. Thor 18. Thor 2 19. Incredible Hulk 20. Iron Man 2
If I watched them all again, I'm sure I'd make several changes.