Whitebeards death for sure. It's not just the panel itself, but everything that built towards it, that makes it hit so hard. From fighting with a chunk of his head missing, to splitting Marineford in two, and being prepared to take on the entirety of the Marines by himself so his crew could escape, all while knocking on deaths door. And then at the end of it all, he didn't even fall to the ground upon dying. Then you get the breakdown of everything it took to kill a man who was already dying even before the war, and it paints the full picture of how much of a Monster this dude was.