I think Fitz, AZ's warm weather/dome, and Whisenhunt's heavy pass offense will be the determining factors in Peyton's decision.
Where ever Manning goes you can bet he will be calling most of the offense at the line of scrimmage and the team will have to build around Manning not the other way around. That discussion was sure a part of the one Manning had with any team he visited. Manning is not Manning if the OC is calling all the plays. That is what makes him special in a no huddle offense.