He can work in both, but IMO he's miles more effective in the 2 man. If they had tried to man mark him in our 4-2-4 it would be much harder. There'd be too much space and not enough help for his marker. They can man mark in a 3 man mid because if Pirlo turns his marker or has a loose first touch, there are 2 extra players in the vicinity to close him quick.
If there is only 1 it is impossible. Pirlo can turn anyone, he would have turned that schlub multiple times yesterday if he had the space. But we had 2 extra guys there bringing their men with them. He even tried a couple times and the 2nd man in would nip him.
If the opposition is intent on having someone on Pirlo, then they will play 4-5-1. If we play 4-3-3 then that extra man (their 5th mid) gets to play infront of their 4 and hound Pirlo. If we move to 4-2-4, then that extra man must play BEHIND their 4 man midfield. If they don't then we have 2 one-on-ones with their CBs and our strikers.
The 4-3-3 is my preferred formation but not because of Pirlo. It will work most of the time but Catania solved it QUICKLY. We should have adjusted as soon as we saw their intention to follow Pirlo around.