No doubt that Arsenal v. ManU will evoke stronger emotions here because this is a site dedicated to the discussion of football/futbol/soccer. However from an objective standpoint there is no question as to which is the bigger game...Colts v. Patriots.
1. History- this is the first time that two undefeated teams have met this late in the NFL season.
2. Impact- an NFL season is 16 games long, losing one NFL game is the equivalent of losing almost two and a half games in the EPL...or taking a 7 point hit in the standings.
3. Even though both the Colts and the Pats are likely to still make the playoffs, there are still huge post-season implications like JDB said, and not all of it is weather related. The fact that the Colts play indoors aside, even if it were two outdoor teams the home team enjoys a clear advantage in the NFL because of the impact that the crowd can have on the game, and I'm not just talking about the emotional impact of 'lifting' the team either. When the visiting team lines up on offense, most fans are saavy enough to know to try and be as loud as possible thereby drowning out the cadence of the quarterback as he's calling the play. In addition to making it difficult for the offense to hear the call from the QB, timing is key..everyone must move at the same time at the snap of the ball or incur either a penalty (for moving too soon) or ceding the advantage to the defense (by reacting too late).
The noise of the crowd affects the ability to hear, forcing the line to look to the QB for visual cues when to snap the ball...can't see ball and QB at the same time so the chances of either a false (early) or late start increases- advantage defense. If you are the home team this can be a huge advantage, especially if you're the Colts since they play in a dome, because then the noise is amplified. Likely the winner of this game will have the homefield advantage throughout the playoffs, meaning every game up until the SuperBowl. That's quite an edge to have on your opponent. By comparison Arsenal v. ManU might as well be for bragging rights. Two great match ups though, and lucky for those of us interested in both, we don't have to choose.