I believe that The Rock vs. Brock Lesnar and The Undertaker vs. John Cena should be the two main events of WrestleMania 29. It's debatable as to which one goes last (although I think it should be Taker vs. Cena), but those are the two matches that should happen, along with probably CM Punk vs. Triple H in the latter's return match.
I think the question here is, does WWE want to take the easy way out and go with the three incredibly predictable main events of Rock vs. Cena II, Undertaker vs. Punk, and Triple H vs. Lesnar? Or do they want to do what I just said and leave the fans completely mind boggled as to who the big winners are going to be?