I say neither. I say the emergence of a young, brash & cocky Shawn Michaels was the bigger story with more potential. Between 1992-1996, nobody was hotter in the company than Shawn Michaels, dare I say, the business itself. You gotta remember, Shawn did it, primarily without the title. He won back to back Royal Rumbles, he headlined two WrestleManias, (WrestleMania XI, a bomb, but it wasn't his fault, he actually had the best match on the card, and of course WrestleMania XII and that classic 60 minute Iron Man match with Bret Hart). No single person in WCW during this period, even dating back to 1991, overall meant more their company than Shawn Michaels did. He had a few Intercontinental Title runs and lest us remember the other classic match of the era that involved Shawn Michaels, The first WWF Ladder Match at WrestleMania X against one of the persons you mentioned, Scott Hall (Razor Ramon). Do you honestly believe Hall would have been as big as he was, and as recognizable if it weren't for that match? Shawn could've had that match with anyone & he still would've gotten that person over. Razor's spots weren't all that great, IMO, but again, Shawn stole the show at WrestleMania and carved out his own legacy.
The Outsiders needed each other more than anything else, and they especially needed Hulk Hogan (as did Hogan need them) during their heyday. This can be proved by the horrific match in Jan. 1999 right after Nash "ended" Goldberg's streak only to fall to a finger poke by Hulk Hogan. Had Nash been playing his cards right, in his favor, he would've held the title longer, broken away from the group to be his own man (ala, Shawn Michaels when he broke up The Rockers) and been a Hall of Famer for sure. I don't think Hall or Nash are worthy of Hall of Fame merit right now, maybe as a team, but certainly not as individuals. The Outsiders were unique at the beginning, but a year or two into their run they became stale, even during a time where fans actually gave stars a chance to impress them over the long haul. I remember watching WCW Nitro less & less around the end of 1997 when---once again---Shawn Michaels became HUGE. The difference in Michaels bringing HHH along vs. Hall & Nash was that even when HHH broke away from Michaels, he still ended up a huge success and one of the best wrestlers ever. Hall & Nash will forever be tied together. In short, the potential to really big massive in WCW died a slow death under the weight of Hulk Hogan. They were never able to be as big in WCW as they should've been.
Now, as far as Ric Flair in 1991, I say he's neck and neck with Hall & Nash. In the WWF during the time, Flair really didn't seem like he belonged. It always seemed odd in a way, maybe because he had worked for Crockett and Turner for the better part of 10+ years. By the time 1991 came along, Flair had all the great matches & feuds he was going to have. He'd wrestled Dusty & Nikita & Luger & Steamboat, Windham & Sting. There was nothing left for him to do, and the potential to have a massive feud with Hogan in HOGAN'S backyard just didn't measure up. It was a dream match that was about 5 or 6 years too late. By then, the wrestling business was on the decline, pretty much everyone had gotten tired of Hogan's act & Flair just wasn't the man he was. Hell, he hadn't been THAT GUY since he last wrestled Ricky Steamboat and won the title back from him. That was Flair's last GREAT match. Everything else, even when Sting won his first title, went downhill (don't believe me, check The Black Scorpion angle. Flair would never have done that during the early to mid 80s. He didn't have to, he was THE MAN).
So in short, I don't believe neither Flair nor Hall & Nash really had much potential, especially over the red hot & controversial Shawn Michaels. Hall & Nash may have had a slight edge over Flair in 1996-97 compared to the Flair in 1991 since we seen all Flair could do, but we were just experiencing the NWO & The Outsiders, but week after week of the same thing got old & they lost their steam. Maybe Hall & Nash did have more potential, but I also think they had the bigger let down. Flair never cost everyone a company, but Nash (maybe not Hall) was somewhat responsible for the beginning of the end of WCW, even if it were unintentional. Ending the company's top draw's streak and then a week later, pulling that crap with Hogan turned off a lot of loyal fans (I was one of them) and it never would be the same again...