Nobody could replace Xavi, there's only one Xavi and there will never be another Xavi. He's the most important Spanish midfielder of all time and one of the all time greats. At this point in his career I have no shame in saying this.
At his peak Pirlo was the only one on this list as good of a passer as Xavi. A less dynamic player but an extremely intelligent one who could have probably fit on this team. Scholes is underrated but the weaker of the three, Xabi Alonso's short passes aren't nearly as good but he is a ridiculous long passer. All great, though Xabi is more of a jack of all trades type who can't really compare with the others when it comes to playmaking.