I wish I could remember what I felt the first time watching the past of the Strawhats (excluding Brook's), Zoro's sacrifice and especially Luffy meeting Blackbeard the very first time, cause I believe some of them would've been part of my list.
However, right out the top of my head?
1.
Where to start? It was literally the moment where all the build up and tension of an entire Saga reached it's climax, where one of the most intense and best coregraphed fights of the entire series came to an end and Luffy ultimately set Robin free of the clutches of the World Goverment. The fight felt not like roller coaster with highs and lows, like Luffy vs Katakuri, Crocodile or Doflamingo, no the entire fight was a high, never have I been more emotionally invested in One Piece than at that moment and yes in this case I can say I actually prefer the anime version.
2.
Forget Ace, real man cried there.
Never would I have thought I'd be so emotionally invested in a ship, which was just about to be burned....Also again, speaking of the anime version.
3.
Just to note, I'm a Luffy fanboy....
I couldn't decide between those two, so I choosed both...
Back then I was already reading the manga for a few years, but outside of casually debating with friends here and there not really going into more depth, so you have to understand that back then before all the Crackers Katakuris and Jacks showed up, Doflamingo seemed not only to be way too important to go down that early in the New World, also it was absolutely unimaginable how Luffy was going to beat that monster with the lousy feats he has shown and when Sanji, who back them was viewed as much closer to Luffy than now and Law have been crushed like they were bugs.. .With later being proven right, Mingo was dominating Luffy with ease for the most part and the Birdcage was slowly closing in, so what was Luffy going to do? He came up with G4 out of nowhere and hyped the majority of the fandom, including me through the roof.
Worst part was, between chapter 783 where Luffy was about to use G4 and chapter 784, where he actually demonstrated it, there happend break which lasted two weeks. So you can probably imagine that the hype and expectations have even been even bigger, also just to remind you that back then g2/3 have been revealed almost a decade ago, hence the theories about G4 were all over the place for years ...However once the chapter dropped and G4 send Mingo flying from the top of the palast all the way down into the middle of Dressrosa, I was left speechless. Luffy has literally gone from being knocked around to fodderize Doflamingo, I was so impressed that I believed G4 was capable of beating even an Admiral lmao.