I give the edge to the Colts. If they can get a running game established and Peyton takes the short passes over the middle and the short outs, he'll keep moving the ball and eventually wear out that Bears D. I don't know much about the Bears secondary but they must be at least pretty decent if the Bear are in the Superbowl, so I'm not counting on much of the long ball. And as long as the Colts D holds up their end of the bargain, by containing Rex, keeping the pressure on him and stuffing up the running game, then that makes him beat them with his arm which is wildly unpredictable.
As for the Bears, their key to winning the game is pressuring Manning. They have to keep him uncomfortable all game and hope that they can get at him enough so that he makes mistakes. Rex needs a good game but if the Bears D is doing its job, then he only needs enough of a good game to manage the clock and between him and his backs, score enough to beat the struggling Colts offense.
In my opinion, whoever has the better running game wins, or if neither teams' running game is able to get going, it's going to come down to turnovers and special teams. The funny thing is, both teams are unpredictable coming into the Superbowl. The Colts could suddenly click on all cylinders and end up blowing out the Bears, which they are easily very capable of doing. On the other hand, the Bears may get one of Rex's outstanding games, and with their punishing D stifling the Colt's offense, the Bears could completely embarrass the Colts in a lop-sided game.
It'll be hard to beat the intensity of the AFC championship this past Sunday, but here's to hoping for both teams playing well. If they do, it will be a great game. Go Colts!