Perhaps as a two, weirdly enough I felt Fletcher-Carrick-Anderson (yes Anderson!!) was one of our most balanced midfield combos and gave us unbelievable control in games, particularly in the Champions League - they complimented each other so well both offensively and defensively, and it felt so comfortable watching us play with them. Incidentally Fletch got a red card just before the final and the balance went out of whack.
With Scholes and Carrick, sometimes you did feel if teams were bold enough to run through the heart of our team, they cut through us like butter due to our lack of mobility in that area, especially as Scholes was slowing down at the time.
Keano and Scholes I'm not mentioning simply because individually talent-wise, they were both frankly incredible and levels above most, so it's no wonder they dominated.
Back to Carrick-Fletcher-Ando though, they just seemed to gel - we'd go away in Europe and just strangle teams. It helps of course when you have the likes of peak Rooney, Ronaldo, and Tevez up front!