Answer: all of the above * (except uh...Dark World, still need to see that one at some point, not in a rush though)
Iron Man 1: Jon Favreau, this man deserves so much credit.
Incredible Hulk: Tim Roth is one of my favorite actors. I was fine with Ang Lee's version.
Iron Man 2: 1st-appearance of Black Widow, 1st-appearance of War Machine, briefcase suit.
Thor: Hawkeye cameo?
Captain America: The First Avenger: authentic introduction of character, I can do this all day, and I love Hugo Weaving.
Avengers 1: Wow from Start to Finish. Can I please watch that again? What, Best Buy has a light-up shadow box!!!!?
Iron Man 3: Rescue confirmed; with sneak peek.
Thor: The Dark World: um...I need to see that at some point. maybe?
Captain America: The Winter Soldier: Holy moly from Start to Finish. Yes, I'll take 3 copies in SteelBook, thank you! Plus a movie poster as well.
Guardians of the Galaxy: Family, and way exceeded my expectations. The music and cast-mix was perfect! Also start of the MCU emotional roller-coaster with feels.
Avengers: Age of Ultron: Awesome from Start to Finish. Oh, what!! You killed off QuickSilver? Bunch of bleep-bleeps!! Nooooo...
Ant-Man: Funny from Start to Finish. I loved Paul Rudd's take on the character, and Michael Pena's Luis stole every scene. He is so good!
Captain America: Civil War: Legends in the Making. From comic books to Ultimate Alliance, now on the Big Screen! Plus, new Spider-Man introduction, OMG! Floored.
Dr. Strange: Very difficult to do well, but they pulled it off. Highlights include the cape, Tilda Swinton, and Mads Mikkelsen.
Guardians of the Galaxy: Vol. 2: one-word: Yondu (you know what I mean...) nuff said.
Spider-Man: Homecoming: I bought the 3D Blu-Ray combo pack for multiple viewings. Need I say more?
Thor Ragnarok: Thor re-booted, thank the Gods..., and thank you Taika Waititi!! Perfect from Start to Finish.
Black Panther: Wakanda FOREVAH!! Shuri and Killmonger were my highlights.
Avengers: Infinity War (part I): Over 25 years in the making. I waited my entire life for this film, ever since Infinity Gauntlet (circa 1992). I left in a mess.
Ant-Man and the Wasp: Evangeline Lilly, Michael Pena, and Paul Rudd. I need them in more films together. Plus the scenes with Cassie, young Hope, and Janet were endearing.
Captain Marvel: Vers, Yon-Rogg, Supreme Intelligence, Kree, Ben Mendelsohn, Carol's story, special effects, and space scenes. And...the music and score...OMG. Even the trailers were amazing!!
Last but not least, Avengers: EndGame: Closure. Absolute perfection. Film-Making at their finest. Now...about that Infinity Gauntlet Blu-Ray Collection... :)