I would go with Flair's 1992 Title Win. Before that the Rumble itself was not a very important event and the actual match was almost like an exhibition, almost meaningless. This was the 1st time a Rumble was a "must see" event (Knowing the WWF Champ would be crowned). Also, the star power representing two decades of wrestling was unreal...Hogan, Flair, Savage,Undertaker, Jake Roberts, HBK, Piper, Sid, DiBiase, not too mention Kerry Von Erich, St Slaughter, Rick Martel, Bulldog, Valentine, it seemed like about half of the biggest stars of two eras combined in this match. The drama was unreal, No one had ever entered among the The 1st Three Contestants and won, and no one had ever lasted an hour. With wrestlers entering the ring at 2 minute intervals (by the time HBK won in 95 it was one minute) you know right away Flair would need to last at least 58 minutes just to make it to the last contestant entry.
The explanantion giving Hogan & Taker "Special Consideration" allowing them to enter among the last ten entries was smart because it heightened the drama of the arrivals, plus protected Hogan from having to work too long. Good move though not saving them for the bitter end, allowing both enough time to do a lot of work and interact with the biggest names, etc.
The best moment is at the 30 minute mark, Flair, visibly exhausted at this point, eliminates Von Erich (in one of his last WWF matches) and Big Boss Man, then collapses in the center of the ring, 30 seconds roughly till the next man is in. When Piper's music hits, the whole arena erupts as Flair, on is knees, looks to the sky as if he's praying with a "Why Me??" look of desperation on his face.
This match also stands out as the first time Hogan is ever really booed. The ending, in which Hogan, angry that Sid eliminated him from behind while he was battling Flair, arguing and distracting Sid allowing Flair to eliminate him was all intended to facilitate a Sid heel turn, the thinking being fans would agree with Hogan that Sid's actions, sneaking up from behind and dumping Hulk, were a betrayal of their tenuous friendship. Problem was the Rumble was heavily promoted as an "Every Man For Himself" event, where fans look forward to see friends battle each other in unique situations. In this match alone we saw Flair turn on fellow Heenan Family member Haku (and pay dearly for it) and battle against Taker, who leading into the event was alligned with him. We'd also seen Hogan battling both Piper & Savage, two former foes who by now he was on good terms with in the storylines. Sid, surprising the 6 ft 8 Hogan when he was distracted by the much smaller Flair and eliminating him made perfect sense, it wasnt a "heel" move, it was a smart move. I'll never forget the chorus of boos that rained down on Hogan afterwards when he confronted Sid, claiming Sid "cost" him the title. As it was played it, Hogan, now eliminated, helped cost Sid the title, his own distractions, which included grabbing angriliy at Sid through the ring ropes which prevented him from seeing Flair move in from behind for the winning elimination. This was the 1st time I ever saw an audience really boo Hogan, Id seen matches where guys like Flair & Savage had a fan base but Hogan overall was cheered. The crowd was split when he faced Ultimate Warrior, although there wasnt a lot of booing in that match. This is the only time the "Real American" Hogan really gets it from a WWF audience. That alone makes this a remarkable event.
The historic nature of Flair's win (1st man ever to win both NWA/WCW & WWF World Titles, 1st Rumble winner to last over an hour and enter among the Top 3 Contestants) and the relative star power (there were 8 former and/or future World Champions in the match, and that doesnt include such top stars as Piper, DiBiase, & Roberts) were both great reasons to remember this match. Hogan getting booed, the first time the WWF Machine underestimated his appeal, was another.
Eventually the Sid heel turn would take effect the old fashion way (he abandoned Hogan in a tag match vs Flair & Taker on Sat Night's Main Event) but Sid himself would fall out of favor with Management and be gone right after WrestleMania.
As far as other memorable moments/matches, I would say the classic match ending confrontation between Taker & HBK has to be included. Two legendary stars, contrasting styles, face to face, in a pretty good battle as the last two in the ring to end the bout. Not as dramatic as Flair vs the whole WWF, but it was a great moment, the crowd was red hot, you could feel the intensity, and every time these two battled in an important match they always put on a great show.