IMO that tops the Bucky Dent HR in 78' because that was a comeback HR, but not a walk-off HR, and there is nothing more thrilling than a walk-off HR in a do-or-die game.
The stakes were also much higher in the Boone Game.
The Dent Game WAS do-or-die, so it was thrilling in that respect, but it didn't end the game and the winner went to the ALCS, not the World Series.
The Boone HR was more like the Bobby Thompson walk-off verses their hated rivals, the Brooklyn Dodgers, followed by the most famous call in baseball history (The Giants win the Pennant, the Giants win the Pennant, the Giants win the Pennant, the Giants win the Pennant, and they're going crazy, they're going crazy!!!!)
Also the Boone walk-off followed a thrilling comeback verses the greatest SP of his generation, Pedro Martinez, who was also the most hated of all Red Sox by Yankees fans because he had a habit of drilling Yankees hitters, but the icing on the cake was the brawl he ignited in Game 3 of the same series, and Pedro tossing Don Zimmer to the ground.
If he wasn't already the most hated Red Sock before that incident, he certainly was afterwards, which made the comeback verses him, Public Enemy #1, a million times sweeter. So the crowd was already in a frenzy, well into the 11th inning, and the tension was unreal ... then Boone went yard on the first pitch of the 11th from Wakefield and Yankee Stadium went insane, as did every Yankee fan on the planet, in bars, their living rooms etc.
The feeling of elation was indescribable. He crushed that ball so you knew it was GAME OVER so long as it stayed fair, and once you realized it was staying fair ... absolute euphoria! ... and Yankee Stadium was off the hook!!
Lastly, it also followed three grueling shutout innings by the greatest closer whoever lived, the Sandman, Mariano Rivera.
Other than the HR itself, the picture that will remain etched in my mind until the day that I die is a completely spent Mariano lying on the pitchers mound in tears. Thats how much that game meant to him, the picture of exhaustion and elation, and this from a man who was famously stoic, rarely showing emotion, win or lose, though of course it was mostly winning from a player who is skating into the Hall of Fame on the first ballot, and it should be unanimous.
Anyway, that Aaron Boone HR is by far my favorite moment ever from the Yankee/Red Sox rivalry.