Torn between Bryan and Batista as Rumble winners.
Batista needs the boost more, if WWE is planning an Orton VS Batista match. His return didn't blow the roof off of the arena. There's no guarantee the fans will rally behind him 100%, if he strolls into Mania as the #1 contender, and Orton is the most logical option for Batista's opponent at Mania. We've already seen Batista VS Cena, Undertaker, and Triple H at Wrestlemania. A match with Punk could work, but they need to turn Batista heel.
Bryan is riding a hot streak now, but we don't know how serious his concussion problems are. For all we know, WWE could do a quick finish at the Rumble, where Bryan locks Bray in the Yes Lock after the bell rings, and Bray taps out in a few seconds to protect Bryan's health. Bryan can come in at the mid to late 20's or #30, and lay low until the right moment, and win the Rumble.
Punk coming in at #1 kills his chances of winning. There's a chance he could make it to the final four, but something (maybe a distraction from Kane, or some other dirty trick from The Authority) is going to happen to further the feud with Triple H, screwing Punk out of a Rumble win.
It's a safe bet Jericho, RVD, and Sheamus will all make surprise returns, but they're not going to win. Sheamus needs to build up some momentum before he faces Orton (as a heel or face). I could picture RVD VS Orton happening in the future, but not at Wrestlemania. And WWE will use Jericho to help put someone else over (see Punk and Fandango) at Wrestlemania XXX.
If he loses the match with Orton, Cena doesn't need a Rumble win, and I'm not 100% sold on Lesnar being in the Rumble. WWE is using Big Show to give Lesnar a boost going into Mania. That's enough, and if Lesnar competes in the Rumble, they're going against his whole "I don't have to follow protocol, or prove anything to anyone for a #1 contender's spot" shtick.