I personally think that Jose Mourinho will be the most successful manager ever, in 10 seasons of competitive football he’s won 7 titles, 2 European Cups, UEFA Cup and also the only manager to win the league in England, Italy and Spain.
I don't think you can compare Fergie with Mourinho tbh, for Fergie to stay and keep Man Utd at the top for as long as he has is an achievement all in its own. Yes Mourinho has done well at multiple different clubs but there's no argument Fergie couldn't of done likewise - thankfully for us though we've had him all to ourselves
Like I said to Tummy previously its impossible to say who's the greatest of all time all you can say is though that Fergie is without doubt one of the greatest of all time