I absolutely hope it doesn't happen, but probably the Patriots.
Unless the Pats are going up against an Eli Manning-led Giants squad in the Super Bowl, they always seem to get the breaks they need to win games, even the ones they have no business winning (see last year's Super Bowl for an example).
What is likely to happen is this...
The game starts out with a feeling out process, where at least one team and maybe both fail to score (at a minimum fail to score a TD) on their first possession or two. Patriots take the lead, Manning leads the Broncos back, the Broncos should win the game, but a talented Patriot such as Gronkowski or Edelman or a defensive or special teams guy comes through and the Patriots take it anyway.
If the Pats win, in the aftermath it will be like 95+ percent of all Pats playoff wins - everyone will give all the credit to Tom Brady, no matter how many mistakes he made or if he just managed not to screw up and other players got them the win.
Even if Gronkowski scores five TDs on short passes where he caught it and then ran through four defenders 30 plus yards to the end zone each time, people will say it was all Brady getting him the ball, even if Gronk was wide open and the worst backup QB in the league could have made the same throws.
If Brady makes mistakes and it doesn't cost them the game and they win anyway, no one will talk about his mistakes, or at least not for long. He could throw four INTs, lostetwo fumbles, have a QB rating of ZERO, and if they somehow eek out a win, it'll be glossed over.
If he makes mistakes and it DOES cost them the game, all the talking heads will make excuses for him. It'll be the fault of his O-line, or the receivers, or someone else. (Example, when they lost the last SB to the Giants, Brady totally blew a throw to a wide open Wes Welker that likely leads to a Patriots win...and most of the talking heads tried to blame Welker.)
Heck, if the game is tied and Brady is trying to lead them down for the winning score and instead throws a pick-six and CAUSES the loss, it'll get blamed on the receiver or the O-line or the coach calling a bad play or the weather wasn't right or Brady sniffed a fart right when he threw the ball and it's the fart's fault cause Brady is too amazing to ever be blamed for anything.
I hope the Broncos win. I hope it happens because Tom Brady royally screws up so badly no one can deny it. But like I said, the Patriots get all the breaks unless they go up against the Giants in the Super Bowl...and the Giants didn't make the playoffs this year, so everyone else is probably screwed.