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Why He'd Fit:
The Cardinals have one of the game's premier wide receivers and no one capable of getting him the ball.
Also, he's Peyton freaking Manning.
The Case for the Cardinals:
The Tennessee Titans and Denver Broncos have their respective hats in the ring, but from an outsider perspective, Arizona makes the most sense.
Denver and Tennessee both have tricky quarterback scenarios that would require major reshuffling were Manning to sign. In addition, both have relatively cold climates (particularly next to Phoenix) and neither has the proven, ace receiver Manning prefers.
Arizona is the only team that checks every box on the Manning list—or at least whatever semblance of a list we can cobble together from various media reports.
As an added bonus, the organization has a track record of working with veteran quarterbacks like Kurt Warner. Coach Ken Whisenhunt did a fantastic job reworking the offense to Warner's strengths and it's fair to assume he can do the same with Manning.
The only on-field concern is Arizona's offensive line, or lack thereof. Though it stands to mention that Manning, through his pre-snap reads and heady play, has been his own best lineman over the years. Finding an All-Pro front five isn't his priority.
*Note: The Manning situation is fluid and fast-changing and it looks like I missed the boat. The latest reports have Denver and Tennessee in the lead and Arizona out. I still don't see it, but apparently those two organizations have Manning's attention.