#1 The Undertaker vs. Seth Rollins
Seth Rollins has been a top guy in the WWE roster for a very long period of time, and as he told Sportskeeda (click on the link above for more information), he has only spent a very limited amount of time in the ring with The Undertaker, and one wonders what could have been, especially in Seth Rollins' current avatar.
There have been so many versions of Seth Rollins over the years, and all of them could have had a fantastic clash with The Undertaker- from the cowardly weaselly man in The Authority to this current Messiah-inspired persona, to the period when he turned babyface and actually took down Brock Lesnar.
Even though Seth Rollins hasn't had the best reputation with regard to working with WWE legends (even though Sting has protested over the years that it wasn't Seth Rollins' fault), Rollins is one of the best in-ring workers ever and can take bumps galore to make anyone look good.
Rollins vs. The Undertaker is totally worthy of a WrestleMania dream match.