Undertaker at WM 29

After the Survivor Series next month, many fans will being making their serious predictions on the WM card.  The big question is, always, who will the Undertaker face this year (assuming he works the show).  My question to you is three-fold:  Who would YOU like to see him face, purely from a fan's perspective?  What is the smartest/most profitable match to book from WWE's perspective (knowing who the champions are now/likely will be and who will be involved at WM)?  Who will the opponent be, no matter what you, or the fans, want?

Personally I'd like to see the Brock match because they can still build Brock up as a believable monster to the point where Undertaker would have to return to take him down.  Plus you know they'd happily beat the s--- out of each other and do cool submission stuff.  I feel like they could do HHH v. Brock at Rumble again, with Brock destroying him again, so that HHH has to go to Undertaker in the ultimate act of desperation to help stop Lesnar.  

Obviously the most profitable would be Rock or Austin returning, but neither is likely to happen.  Barring that, Cena is the biggest upper level guy they've got left to throw at him.  
My gut says he's just taking this year off, though.  There's no opponents ready for him and not otherwise occupied, and they don't need the match with Rock-Cena and HHH-Brock headlining the show.