You know what Rotten Tomatoes is great for? Settling arguments of taste. And are any arguments of taste more incendiary than the correct ranking of MCU films? No. No debate is as likely to result in foaming-at-the-mouth rage, ruined friendships, and disowned children. If you're in the middle of a knock-down, drag-out brawl over whether Avengers: Endgame is superior to Infinity War, you can always use the thousands of votes cast by fans on Ranker's own roundup of the best MCU movies.
If, however, the argument can only be settled with the illusion of authority provided by Rotten Tomatoes, then, well, fine. Here it is, in descending order according to the all-powerful Tomatometer, with scores from the review aggregator's audience included and considered only in instances of ties, when two films share a Tomatometer score.
Tomatometer score: 79%