First off, allow me to say that I was completely, totally wrong in my repeated claims that Manning was not going to get anywhere near as much money from any other team than he was going to get from the Colts because of his age and injury status. Turns out that Manning actually benefited financially from the Colts' releasing him! I was wrong, I am an idiot, sorry.
But folks who claim that Manning chose Denver over San Francisco "for the money" instead of choosing a superior path to a title are off base. Now granted, San Francisco is a better, more talented team. However, there are lots of talented teams in the NFL, and only one "Super Bowl caliber team" can win a Super Bowl in any given year. Maximizing your chances of winning a Super Bowl is less about being on the best team than it is having the best path.
The reason for this is the nature of playoff football. If your team has a slight dip in performance (i.e. due to injuries) or your opponent plays slightly above their heads, you are going to lose even if you have an arguably superior team. If anyone knows this, it is Manning and his 19 career playoff games, a lot of them against the likes of the New England Patriots, Pittsburgh Steelers and San Diego Chargers when those teams were playing some of their best ball of the season, and his own team arguably wasn't.
So, you are better off in a playoff field where there are going to be fewer strong teams. You can put a very good team in a bracket with the #4, #5 and #6 seeds, and a great team in a bracket with the #1, #2 and #3 seeds, and more often than not, the very good team has the better shot of making the title game than the great team. And right now, there are simply more strong playoff-contending teams in the NFC than the AFC.
Let's go by division. The AFC West and the NFC West are a wash: they both stink. So, Manning choosing an AFC West team over an NFC West team is about the same. Except that the NFC West has the POTENTIAL to be better. The Rams have Sam Bradford plus a bunch of draft picks coming their way by trading Robert Griffin III. The Seahawks and Cardinals are both talented clubs whose main deficit is at quarterback, which they might address at any time (and the Seahawks may have already done so with Matt Flynn). Meanwhile, the Raiders are rebuilding, and the Chargers are a total mess. So while the NFC West may become competitive as soon as this season, the AFC West will be Denver and everybody else for at least the next 2 seasons, possibly longer. Advantage (for Manning anyway): AFC West.
AFC South versus NFC South? The NFC South has Super Bowl contender New Orleans, playoffs regular Atlanta, a very intriguing Carolina, and a Bucs team that would be a lot more successful were they in the AFC or NFC West. The AFC South? Rebuilding Titans, rebuilding Colts, rebuilding Jaguars, and the Texans ... hey YOU go count on Matt Schaub, ok? Advantage (for Manning): AFC South, big time.
AFC North versus NFC North? Title contenders Green Bay, playoff contenders with young Pro Bowl caliber QBs and strong defenses Chicago and Detroit. Rebuilding Minnesota is the only dead weight. AFC North? Pittsburgh is capped out and aging, and so is Baltimore, whose window is about to close. The Bengals are young and talented, but I think that Manning is pretty confident in his ability to outperform Andy Dalton in a playoff matchup. And the Browns are actually worse than the Vikings. Advantage (for Manning): AFC North.
AFC East versus NFC East? Giants: Super Bowl contenders. Cowboys and Eagles: playoff contenders. Redskins: better than a lot of other division cellar-dwellers. Compare that to Miami (no QB, just traded their only good WR, Reggie Bush at WR, just lost excellent DC Mike Nolan), the Jets (declining defense, Mark Sanchez at QB, RBs and WRs average) and Buffalo (who let's face it would be thrilled to just make the playoffs at this point). Sure, New England is still there, but Tom Brady is aging, and he has no real playmakers at RB and WR, and the defense is a liability. Advantage (for Manning): AFC East.
So where in the NFC you actually have more playoff caliber teams than playoff spots (the 10-6 Giants and 10-6 Bucs missed the playoffs in 2010 for example, and another situation like that might have happened in 2011 with the Bears and Eagles had it not been for QB injuries) in the AFC last year you had Andy Dalton, T.J. Yates and Tim Tebow leading teams to the playoffs, with the latter 3 winning their division.
Granted, things do change in the NFL, and quickly. But it is safe to say that for the next 2-3 years, Manning has a much better chance of making the playoffs and advancing in the AFC - and especially the AFC West - than in the NFC. That makes a Denver team with a good defense, OL, running game, coaching staff and front office, and probably only a WR and TE away in the passing game a better fit for Manning than almost any NFC team.
So, Team Manning made the right choice. Good for them.