Oohhh, looks like I tied it for the Joker...
I think Joker owned the year for a couple of reasons:
1. It's a "serious" movie, that aspires to "elevate" pop-culture beyond its comic-book origins, while Endgame really is "just" pop-culture, a popcorn movie event that has no real resonance
2. From almost every single point of view of crafting, it is a much better artistic endeavour than Endgame (photography, acting, music, editing, directing...) and finally
3. While Endgame touches on "serious" topics (how to deal with loss and grief, the meaning of friendship and sacrifice...), Joker hit a nerve with its look into mental health, disenfranchisement, loneliness and the general disillusionment with the state of the world.
In general, I feel that the discussions the Joker sparked around the globe and in the media are miles ahead and much more profound than anything that Endgame sparked. Endgame is a milestone because it ends a 23 movie, 11 year cycle, but I think that will be its only lasting legacy. I believe Joker is a fundamentally better, more intelligent, deeper movie.