I think it's Bryan/Rollins at Mania. Rollins cashes in on Cena, Bryan wins the Rumble, Seth uses the Authority to be a roadblock for Bryan again, Bryan overcomes them again and beats Rollins at Mania for the title. Sure it's only a two month reign for Rollins, but he could have a longer reign further down the road.
Considering that I think the Front Office would rather troll DB fans, it's almost more likely that they do have him win, then have him beat Brock, only for Rollins to cash in on him immediately and win.
The only question there is if that would ruin Rollins...
Alternatively, they could have Rollins fail his cash-in, but still have a legitimate claim to a match with Bryan, since in this scenario, he would've been foiled by a third party.