#1 Andre the Giant vs Hulk Hogan, WrestleMania 3

When Jesse Ventura claimed that this was the biggest match in history, it was not hyperbole. It can be argued that this WWE title match at WrestleMania III was the most important match ever up to that point.
WWE had built Andre as an undefeated (which was not officially true), and unstoppable machine and his heel turn in order to get his shot at Hogan's title was classic. So we had an "undefeated" Superstar (for 15 years no less) and the champion for three years going one on one to settle a grudge born out of Andre's jealousy for Hulk Hogan.
There were, however, downsides in terms of calling this an all-time important match. Firstly, the match were not great from an in-ring standpoint. Secondly, the match went towards establishing Hogan as a star; the problem with that being Hogan was already a bigger star (or close to it) than Andre at that point, which meant that the job the match was supposed to do was already done.
However, this same match was the main event of the Pay-Per-View that showed that wrestling had arrived. Even if the 93,000 people that WWE stated attended the event was overstated, there was still well over 80000 people there, and a lot of them were there to see the ultimate clash of the Titans.