The 90-91 Rebs loss to Duke has been ranked in several top 10 lists of the greatest upsets of all-time. It was essentially the same matchup as the 1990 championship, scarred with numerous claims of UNLV throwing the game (just google UNLV Hot Tub), bizarre circumstances (UNLV's point guard fouled out for the first time all season and the final shot of the game was a bizarre 18 foot jumper which was the opposite of UNLV's style), and even Coach K admitting it took a miracle for Duke to win that game.
Bobby Hurley was asked who would win a hypothetical matchup between the UNLV team and the Fab 5 and his response, “It’s NOT EVEN close…Vegas would’ve beaten them easily…If the Fab Five stayed until their Senior year, they (UNLV) still would’ve beaten them. Vegas was the closest thing to an NBA team.”
A great analysis of pitting the best against the best is found here:
All-TimeTop15CollegeBasketballTeams
The fans on rivals voted and the results are here:
Fan perspective: Top ten college basketball teams of the all time - College Basketball - Rivals.com
Yet another opinion, though this one favors the '91 team:
TheDraftReview - 1991 UNLV: Best College Basketball Team Ever!
I could do this all day:
5 Greatest College Basketball Teams of the Modern Era