I did a thread talking about everyone's least favorite crossover and Civil War 2 won in a runaway vote. Other contenders were Avengers Vs. X-Men, Age of Ultron, Secret Empire, and my personal choice Secret Wars 2.
But enough negativity! What is your favorite major crossover/event? I obviously cannot list all of them so I will try to use the Wikipedia article, and what I have inferred are the most well liked crossovers, in making this list. I'm also limiting to "Marvel" events as opposed Spider-Man or X-Men though with something like Absolute Carnage I was not sure if that counted. Because I think that was firmly a Venom event, I did not include it.
The list:
1. Secret Wars 1984
2. Atlantis Attacks
3. Acts of Vengeance
4. The Infinity Gauntlet
5. House of M
6. Civil War
7. Annihilation
8. Secret Invasion
9. Siege
10. Original Sin
11. Infinity
12. Secret Wars 2015
13. War of the Realms
14. Empyre
15. Other - Which one?
My favorite is Secret Wars by Hickman followed closely by the first Annihilation. I have a soft spot for the original Secret Wars...but it's not very good. I've never loved Infinity Gauntlet as much as everyone else but it's clearly good and its another one I have a soft spot for as it was one of my first TPBs. I think Secret Invasion is the best event Bendis was a part of and I think War of Realms was a solid wham bam climax to Aaron's Thor run. But yeah, it's Secret Wars 2015 and Annihilation for me. Both were wonderfully executed.