If WWE wants to match him up with a heel that he has never faced before then Wyatt is the best choice assuming they are able to keep Wyatt a heel until next year's WrestleMania. That may be difficult considering he has the fans singing along with him, which is not a heel thing, but it's in the best interests of the company that he remains a heel because they need him in that role. They have enough babyfaces already. Wyatt's a guy in his mid to late 20s that is a star on the rise. He's going to be a main eventer one day, so he's the perfect kind of guy to benefit from working a big match with Undertaker. There would be a question of who goes over in the match because if Wyatt won it would be a huge boost to him as a younger wrestler. If they built it up as a heel attacking the face, though, it would make more sense for Undertaker to win it. My feeling is that if Undertaker wants to work a competitive match with a younger heel that could be elevated just by being in the ring with him then Wyatt is a great choice. Win or lose, Wyatt would benefit from it.