For me it'd have to be one of Ronaldo or De Gea.
I am a big believer in the fact that the importance of the captaincy in football is largely somewhat overstated in this day and age when it comes to actually impacting performance on the pitch. You hand the captain's armband to mostly anyone on the City team and it's not going to prevent them for challenging for titles. Likewise, you hand the captain's armband to mostly anyone in our current setup and it won't make us a coherent unit.
In the days where tactics and training were less sophisticated, having a great leader on the pitch probably made a much greater difference to a side's fortune, since one man might be more capable of galvanising a team and dragging them to victory through sheer force of will. Nowadays, the very best sides have patterns of play so well-drilled in training that you simply cannot rely on one man to be ordering the side around. You would get ruthlessly exposed by any competent unit. The days of "Captain Fantastic" heroically leading his team to glory are, in my view, past us.
So having said all of that, why do I think we should give the captaincy to Ronaldo or De Gea? Why not just leave it with Maguire? Well, for me it has to do with pressure.
When people get angry, as we fans are right now at the team's performance, a natural reaction is to play the blame game. To use a term often banded around here, it's often popular to pick out a "scapegoat". Harry Maguire came to the club with a world-record transfer fee but without the pedigree within the game to back that up. Before he'd been able to properly embed himself at the club and endear himself to the fans, he was also made captain. And on top of all that, his form this season has been truly terrible. He is almost the perfect lightning rod for the anger that we're feeling at the team's performances right now, and given all of this it is not difficult to imagine that his stress levels are through the roof.
One massive mistake Solskjaer made in handing the captaincy to Maguire was failing to realise that, when the team is going through a rough patch, a crucial role for the captain is to provide a bridge between a disheartened team and a fanbase that probably is not warming to them. For that reason, one thing that is absolutely essential for any captain is that they have built up ample credit with the fans themselves. Maguire had only been at the club six months when the decision was made to give him the armband, and his pedigree was not sufficient to overcome that.
Right now, I don't think we need a captain who will shout and holler at the players, ordering them around. We just need someone to provide reassurance to a fanbase that has lost all love for its team. It has to be someone who the fans had grown to like prior to this shitshow, and for me the only two that fit the bill are Ronaldo and De Gea.