This is a tough one; tough, in the sense that Scholes would definitely finish bottom of the pile, as he is a level below Riquelme/Xavi/Pirlo.
However, when it comes to the other 3, there is so little to choose between them. All 3 are absolutely wonderful players. I'd go with Pirlo as my top pick (only cuz I'm biased). I wouldn't be able to choose between Xavi and Riquelme though.
Throw Zidane into the mix though, and there could only be one winner