Nice move by the 49ers. As for PM heres how it boils down.
If Manning wants a clear path to the SB he should choose the 49ers, does he want that pressure? He might you never know.
If he wants a challenge with a coaching staff & front office he likes he should pick the Broncos
If he wants a challenge with familiarity of the are and be the "hometown hero" he should pick the Titans, does he wanna stick to the Colts fans twice a year by beating them down? I don't know about that one.
I think its anyone's game, but if Peyton isn't going to shy away from the pressure he should go to the 49ers. They will be Superbowl favorites and if they don't reach the SB it will be viewed as a failure. The media attention there will be insane also, remember hes coming from a town like Indy. Coach Harbaugh will likely clash with Manning both of them are fiery guys who want to run sh*t so if they don't have a great season year one or two its probably not going to end well. Lots of things working for 49ers and some work against it.