For people searching for advice on this topic, as I did recently, I can say that playing a fluid and attacking tactic through the whole game has given me two victories against City in my first season with United. Playing a 4-4-2 along the flanks with a very high defensive line, quick tempo and wide play I managed a 4-2 victory at home and a 2-1 away. This is with a City team who have 77 points for 32 matches, and a GD of 61, only beaten by myself with 83 points for 32 games and a GD of 63. They have more than one 7-0 victory in their campaign, and are looking as possible winners of CL.
Edit:
Another point with the high defensive line is, that they only created one actual chance in the 2-1 victory, which obviously resulted in a goal from Tevez.