I Think the answer is based on the fact that they have Messi as well. My answer would be Iniesta, but not because he was the worst, i Think they’re all around the same caliber of player. Theres never Been a better player in (recent) history to play the Busquets role as defensive midfielder+ball progressor. The same Can arguably be Said for Xavi as a tempocontroller/playmaker. Iniesta shared the tempo-controlling responsibilities with Xavi, but also had more final 3rd responsibility, with breaking the opponents defensive structure with his dribbling (a delicious croquets here or there) and final 3rd passes. A lot of this responsibility was also handled by Messi. So in an alternative world we would have a player who maybe doesn’t have the tempo-Controlling and security of Iniesta but was even better in the final third (high ask, I know) to alleviate Messi of this responsibility and allow him to focus more solely on end product. But it would have to be someone who was also secure in possession as well as the game plan hinges on that.

The introduction of Fabregas I think was a step in this direction. Thiago being equally talented but more in the mould of Xavi (and down the pecking order) and then shipped out.

My answer to this would be someone like De Bruyne, Zidane, Maradonna (but maybe not him as he and Messi would fulfill the same role as main man).