I'm better than Mangala but regarding your general question, who is better for City and who is better for another team isn't always going to be the same. City aren't a side that are going to be on the back foot, camped in their 18 yard box defending crosses and balls into the box. Now Maguire's more than just a lump that will head things away but he's not as good on the ball as either Otamendi or Stones.
That said Maguire's definitely capable of playing for any of the top 4-6 sides, the issue is the price though. Paying the talked about £70-90m you'd be expecting to sign somebody that would walk into the side and be a guaranteed starter, if not a massive upgrade on what you've got. I don't think you could say with any certainty that Maguire would be a guaranteed starter for any of Chelsea, Spurs, City or Liverpool. Only at Utd and Arsenal would he be that and that would be because their defence's are ****.