I played the 3N-3W-2N-1-1 today. Loved every second of it. Scored two goals. Took off my DMC and put on my AML for a bfly formation and scored three more.
Used the typical defensive tactics, through the middle with red forward arrows on AMC & DMC.
As for the "Most defensive formation"? It doesn't exist. Do you want to overload midfield? Do you want your strikers to have all kinds of ball time? Do you just want to tackle the ball carrier all game long?