From an overall perspective, I'd much rather see Wade Barrett take on Taker than Big Zeke. Overall, Barrett is an infinitely better wrestler, he's significantly younger than Zeke, more athletic and has the promo ability to get fans interested in a match with Taker. Barrett is no longer in the main event picture at this time, but his time as leader of Nexus and his feuds with John Cena & Randy Orton show that Barrett has the potential to be a main event level talent in the long run a little later on down the line.
To be fair, Big Zeke is one of the better powerhouse wrestlers to come along in a long time. He's a big, thick 300 pound slab of muscle with legitimately freakish strength to go along with it. And, generally speaking, he's somewhat decent on the microphone. He actually had a pretty decent match against Big Show on SmackDown! last Friday. It was about 3.5 minutes and while it was far from an all time classic, you've got to compliment someone that can get halfway decent match out of the Big Show. The thing with Big Zeke is, in my opinion, there's just not really any long term money to be made off the guy. In some ways, I can buy him as a guy that, like Big Show, could be a staple in the WWE mid-card scene and can provide some memorable moments here and there. I just hope that they don't make the same mistake as they did with Show and give Zeke World Title runs. In order for Big Zeke to even come across as someone that most fans would be interested in seeing take on The Undertaker at WM, he'd have to get a push and be booked along similar lines of John Cena. He'd have to be pushed to the moon & stars, he'd have to get huge victories over big names in the WWE and do it decisively. And, even then, there's no real guarantee that people are really gonna get excited. With the past three WrestleManias, the WWE has set an extremely high standard for Taker's matches. All three were huge, big money matches and, quite frankly, Zeke isn't in that league and it'd take longer than the next 11 months or so to get him at that league.
I don't look for it to be Wade Barrett either, though I think he has a much better shot and would give an altogether better match against Taker. For Barrett to be a viable challenger, the WWE is gonna really have to put some focus on him over the next 6 months.