I think the 49ers have an excellent chance to get Manning, but as a fan of the team, I really hope they don’t.
I think their chances are good, because while everyone has speculated on which team would benefit the most from Manning, the real question is which team would Manning most benefit from? He’s the one who decides where he wants to go. I think his priority is getting to another SB, and the 49ers clearly give him the best chance of any team left now, or for that matter, any team under original consideration. They barely missed the SB last year, and even without Manning would be a contender this year, with a strong defense and solid running game. All they lack is a more prolific passing game. They have one weapon for Manning in Vernon Davis, and maybe another in Randy Moss (though I think that might have been a bad signing, too. I liken it to another Bay Area signing of an aging former superstar with character issues, Manny Ramirez with the A’s).
That said, I think signing Manning would be a big mistake for SF. In the rush to grab him, some people seem to forget that while Manning, if healthy, could turn any team into a playoff contender, it’s far more difficult to go from playoff contender to SB. We saw just this past season how much of a role luck plays in getting to the SB. Even with Manning, there is no team in the NFL that could aspire to a more potent offense than GB and NO had, and yet neither team even made the title game. Granted, poor defense made a big difference, but it’s also a matter of peaking at the right time. The 49ers with Manning might go 15-1, and still have that one bad game in the playoffs. Manning at his peak can essentially guarantee that a team gets into the playoffs, but after that it’s somewhat of a crapshoot.
This becomes especially a problem with Manning, because his postseason performance has been erratic. He has played brilliantly some times, but poorly at others. I think he was 9-10 in the postseason with Indy. In most of those ten losses, the Colts were favored, and in most of them, it was the offense that disappointed.
In the best case scenario, he probably has three more good years left. He might lead the 49ers to the SB in that time, but if he doesn’t, then the decision to sign him becomes a bad one. In that case, they did no better than they would have with Smith, and are left with no likely QB prospect, and probably no high draft pick to get one (they would presumably keep Kaepernik, but I don't know how much potential he has to be a starting QB). And even if he does get them a SB, Smith might, too.
I think he’s a much better fit for Tennessee. They benefit in two ways. First, he will definitely turn the team into a strong playoff contender (from the fringe contender status they exhibited this year). And second, Manning gives Locker a chance to learn from him and develop, so they don’t sacrifice their long-term prospects at QB. It seems to me that’s the key to all of this. Then, even if you don’t get to the SB (or if it turns out Manning can't come back to 100%, gets injured, etc), you haven’t lost anything except some money.
Denver would not be as good from that POV as Tennessee, but better than the 49ers. I don’t think they could keep Tebow as backup, because his style is so different from Manning’s. A backup QB has to be able to run the same offense as the main guy, and Tebow couldn’t do that. But dumping Tebow might not be a bad decision even without Manning, so Denver has less to lose than the 49ers. And like Tennesse and unlike the 49ers, they would have little chance of getting to the SB without a QB upgrade.