A lot of good arguments have been made here for the best rivalry in pro wrestling.
Given the subject, we should look at what makes a rivalry great. In my mind, a great rivalry can do two main things:
1) Sell a crowd and a television audience.
2) Elevate the status of a professional wrestler.
The greatest rivalries are not those by two established wrestlers. Hogan and Savage had some excellent bouts in the late 80's, but I wouldn't consider their rivalry great; the same with Hogan vs. Andre the Giant. While a colossal match, I would hardly consider it a rivalry.
A well-placed rivalry moves a midcard face or heel who is gaining momentum into the main event and their talent may in fact keep them there—Cena's feud last summer with Sheamus and The Miz are prime examples.
But what rivalry had the most impact? Which one left the biggest impression on a superstar and moved them into the main event picture for years? Even a decade?
The main one that comes to my mind is Ric Flair vs. Sting.
Steve Borden, AKA Sting, began his wrestling career sometime in the mid-80's, teaming with the Ultimate Warrior to form a short lived Tag Team called The Blade Runners. Nothing much happened with the team and Sting became a singles competitor for the Universal Wrestling Federation in 1986.
Sting caught the eye of many backstage talent and was one of Dusty Rhodes's main projects when Jim Crockette of NWA/WCW bought out the UWF.
Rhodes booked Sting in Cockette's first pay-per-view event, Starcade '87 in a six-man tag match with the Fabulous Freebirds. In 1988, Sting was becoming a main face in the NWA/WCW when he was booked for an angle with Ric Flair. This culminated at Clash of the Champions, a wrestling showcase featured on TBS to compete freely and airing at the same time as Wreslemania IV.
Now, for poor kids like me that couldn't afford a Wrestlemania PPV, being able to watch wrestling on a Sunday, particularly THE Sunday, was a wonderful experience.
The stipulations of the match were silly. JJ Dillon, Flair's manager, was suspended from a cage to prevent interference, and a panel of 3 judges—some Penthouse Pet, Jason Hervey from the Wonder Years (now known as the director of many of the TNA Backstage and Reaction segments) and somebody from Leave it To Beaver—were chosen to determine a winner.
Given these ridiculous conditions, that Sunday afternoon, a star was born after a 45 minute time limit draw (one of the Judges chose 'tie'). Sting was the top face of the new era of NWA/WCW, which would eventually become WCW.
I encourage you, if you have time, to watch the entire match. It is one of the best matches ever.
Sting continued to feud with other members of The Four Horsemen before gaining his first singles belt, the NWA Television Title, from Mike Rotunda in early '89. Still, Sting and Flair continued on their back and forth rivalry, culminating in the ironic joining of Sting with the Four Horsemen after Flair was attacked by the Great Muta, only to be rescued by Muta's rival at the time, Sting.
In shades of what the WWE would do with Evolution 15 years later, Sting won a round robin tournament at Starcade '89, by beating his then stable partner Ric Flair and became number one contender for the World Heavyweight Championship.
Like Evolution, Sting was pressed to give up his No. 1 status by other members of the Horsemen, and when Sting wouldn't relinquish, he was beat down and kicked out of the group.
The rivalry was put on hold due to a knee injury, placing Lex Luger in the World Heavyweight picture until Sting recouped. It is reported that Flair refused to drop the belt to Luger, who he felt was a lesser talent and the momentum built between him and Sting would be lost. Flair had a lot of respect for Sting, and this move proved to be a great one on the part of NWA/WCW.
Once Sting was back, he was placed right in the Main Event picture. Sting faced more attacks by the Four Horsemen and again, in ridiculous fashion, was rescued by Robocop.
The push eventually lead to Sting's capturing of the World Heavyweight Championship against Flair at the Great American Bash in 1990.
(The 1990 rivalry can be found here in a short 7 minute clip).
The rivalry continued with Flair playing the role of a masked annoyance to Sting's title run as The Black Scorpion. Sting's run eventually ended in January of '91 with Flair regaining the title from Sting.
In the early 90's, WCW broke away from the NWA and became its own promotion, recognizing Flair as the first WCW World Heavyweight Champion. Regardless of his loss, Sting was still the top face of WCW and would continue to be for the next decade.
Flair eventually left for the WWF in 1991 but returned in 1993, still in possession of "The Big Gold Belt." The politics of wrestling created a situation with WCW, who broke way from the NWA and coined a new "International World Heavyweight Championship" in contrast to the World Heavyweight Championship.
When these two belts were unified, it was against World Heavyweight Champion Ric Flair and International Heavyweight Champion Sting.
At every pivotal point in the WCW, regardless of the NWO and what it created in the 90's, there was always Sting and there was always Flair.
Sting and Flair headlined the first Nitro in 1995. Though Randy Savage won the WCW World Heavyweight Championship in a Battle Royal at World War 3 1995, it was Sting and Flair that stole the main event.
When Flair formed a face faction to battle the NWO in 1996, it was the Crow-faced, trench coat wearing Sting who came to help, only to turn his team down because of their distrust in him. Sting went from being the top face to the top mystery, and and fans waited breathlessly for months before Sting finally took the bat to the NWO and took the bat to the WWF's ratings.
WCW was king, at the time, and this was in large part due to Sting's face foil against the NWO and the eventual formation of NWO Wolfpac. But lest we forget, there would be no Sting without a Ric Flair.
Like Yin and Yang, one always seemed to need the other, and WCW understood this.
When the company eventually was bought by the WWF in 2000, the last Monday Nitro featured Sting vs. Ric Flair as the main event, with Sting winning the match, and both men embracing after the match.
Regardless of who WCW bought from the WWF, these two were the face of WCW and they knew it.
Flair went on to work with the WWE/WWF and is currently in TNA; Sting became involved in TNA after 2003.
Sting never went on to wrestle with the WWE, but if one is asked who the most popular wrestler of the modern era is to never had wrestled in the WWE, everybody would say Sting. He may be the last real superstar to not have had a stint in the WWE, monopolies and competition in wrestling not being what it was 15 years ago.
He is an icon and a legend in the sport. And he is this way because of a 45 minute time limit draw against Ric Flair in 1988.
Ric Flair and Sting: The greatest rivalry in pro wrestling.