At this time?
After what I saw, this weekend, Man City completely dominating the game against Chelsea, despite having only scored one goal, I think that at the moment there is no really very difficult opponent for Man City in the Premier League.

I believed that Chelsea were the team that would cause the most difficulties. But he spent most of the time playing on the counterattack, and leaning against his area, without creating great opportunities. I don't see, at the moment, other teams doing what Chelsea couldn't do.