The winner and #1 MCU phase 1-3 film is: Avengers: Endgame
Highest ranking: #1 (TheLetterM, DreamTeam, axeman90210, Adami)
Lowest ranking: #5: (DarkChestofWonders, jammindude)
Stats of note: As mentioned, this finished in the top 5 on every single list. There were 4 first place finishes, 9 second place finishes, 1 third place, 1 fourth place, and 2 fifth place. This was clearly a favorite. But that said, it would have finished second to Infinity War if not for the #12 vote it got.
I've not had a lot of time to really sit down and type out my thoughts on this one yet, but I'll briefly go over my feelings on this one, It definitely has been a flip-flop coin-toss between IW and Endgame for me, but I think the latter has eventually settled into being just slightly better, and as others have said, it's more of a 1a & 1b situation. Both Infinity War and Endgame are really a 5.5 hour epic that feels inseparable, and for me, it's hard to watch one without the other. Considering they feature the same directors and writers, were filmed back-to-back, and are so much more related to each other than any other two films in the entire MCU franchise, it's really hard to view them as separate entities, but Endgame really wrapped everything up that had been building up for 11 years over 21 previous movies.
The opening act was a bone-chilling re-introduction to the characters and their predicaments post-IW. How did they handle losing half of the universe? Who was left? What happened to Tony and Nebula stuck on Titan? Everything felt answered so quickly and easily that when the FIVE YEARS LATER title card came up, it was such a shock. I still recall the audible gasps in my theater, and it was pretty quiet for awhile until Ant-Man showed back up. Then it was a race towards Act 2 - the Time Heist - every MCU diehard's wet dream, full of Easter Eggs, references, callbacks, and so much more, including even MORE unique and fun character interactions, like Scott and Tony, Rhodes and Nebula, Bruce and the Ancient One, Thor and Rocket and seeing Frigga again! Every part of the second act was just a gold mine for fans who had been around since the beginning and experiencing these moments from previous years and films but in different aspects. Of course, the shock of losing Nat will never wear off, and I'm glad that hasn't been forgotten (Black Widow post-credits scene and Hawkeye series). Of course, Hulk's snap was another big moment too, and everyone in my theater was in awe, but then when Thanos arrived, and all hell broke loose, I was on the edge of my seat from there on out.
That third act... hoo boy, I could write for DAYS about it, but I'll keep it short since a lot of others here have already praised it where praise is deserved. This was a final battle I had not seen since the likes of LOTR: The Return Of The King's climax, but with characters I've grown to love for over a decade. And all of the little moments between characters in there are so charming, like T'Challa calling out Clint's name, or seeing Giant-Man just lay into a Chitauri Leviathan. I could watch that last act over and over and still be entertained. Of course, when Tony snapped, everyone in my theater was in tears or sniffling. Definitely one of the most emotional moments in MCU history, and it'd be hard for them to top something like that. They'd have to actually kill of Peter Parker or Thor or Hawkeye to MAYBE get a similar reaction, but it won't be as big I'm sure. Or they could just kill off Tony again! Hurray for variants!
Lastly, I'll see that as optimistic as I am about The Kang Dynasty and Secret Wars, I feel like Endgame may still top both of those, but I could be wrong. The emotional investment and build-up between IW/Endgame was unprecedented, and it'll take a lot for me to feel like that again. I guess we will have to wait and see if the next 3-4 years of films can do it!
-Marc.