There's not really much competition now for the Man U job. It seems that too many candidates are too damaged from their numerous sackings they've effectively ruled themselves out. Even Martin O'Neil is doing his best to ruin any chance he had.
I know - O'Neill is no longer a young, up-and-coming manager witha great record.
He has been moderately successful at some clubs but seems to be getting worse with age. Can't see Man Utd wanting to poach the manager of the 4th bottom side.
Guadiola is an unknown quantity outside Barcalona - I can't see him in the Prem apart from at Aresnal, but I think employing him would be a huge gamble.
Mourinho, on the other hand, is proven in multiple leagues including the Prem and I'm sure Man City et al will always have him top of the list