#1 Sting
Topping this list is the WWE Hall of Famer, Sting, who has been clamoring for a dream match between himself and The Undertaker for the longest time. Fans have been asking for a dream match between the two since the Monday Night Wars era in which The Phenom as well as The Icon did their best to support their respective promotions stay afloat. Moreover, their Goth personas added to the appeal of a potential encounter between the two.
While The Undertaker proved his loyalty to WWF (now WWE), Sting did the same for WCW. After the latter went out of business, Sting was concerned about WWF not protecting his legacy and thus, he decided not to sign with the sports entertainment giant.
After wrestling for different promotions including TNA/Impact Wrestling, Sting signed with WWE in 2014. But in the words of The Icon, it wasn't possible to book a match between the two then. Sting told Fite TV.
"I mean, everyone knows who it would be. Taker, he’s the only guy I’d come out of retirement for now. No one else. We could just never get it together to make it happen. When I started talking to WWE he was booked with Brock and then I did the deal with Triple H and he had another feud going on at the time, so it was just one of those things we couldn’t make happen."
With The Undertaker announcing his retirement and Sting unable to get cleared to compete, there's absolutely no way this match could take place now, no matter how much the latter or us fans want(ed) it to happen. Even The Undertaker admitted recently that he no longer has the skill set to make the dream match as great as fans want it to be.