Yes, English football is not Valencia. As
@prarek wrote before Valencia have sacked Hiddink, Ranieri, Koeman and Quique Flores in the past, it has been a crazy team for years.
He seems an intelligent person,with the knowledge , but he has chosen very bad his first destination.
Karanka(he would be one of my candidates for United) was assistant coach for three years with Mourinho and had been before in the Spanish National team, but when he left Madrid ,did not get into the mud as Neville, but went to a small team .
Neville knows the club and certainly is well aware of his weaknesses. Guardiola is going to spend a lot of money and in my opinion will easily win the league. With the current squad United have no choice. In my opinion the only option is United / Chelsea + 300 million in signings with some defensive pragmatic coach who perhaps would get hold until the final weeks, parking the bus ,however the concept will not change: City has the most technical players and the most fashionable coach. It is the handsome team.
To sign Mourinho for me would be like going home with the ugly girl of the party because the pretty one has said no, and the same for all those defensive managers, as we say in spanish, would be "bread for today and hunger for tomorrow". Between Giggs and Neville, the second gives me better feelings. Perhaps you wouldn´t win Premier inmediately but I think he could thrill the fans and organize the club pretty well.