I think formation should be defined by the players. If you're starting 11 has 5 midfielders then it's 4-5-1, but should you have two strikers that can't play anywhere else, then 4-4-2 it is. We saw a midfield diamond on Saturday not because AM wanted to try it, or at least not mainly, but because the players in form that he wanted to pick suited that formation best.
So, if you want to look for our best formation, look at our best 11. The keeper and flat back 4 pretty much pick themselves, as do Bent and Gabby, wheteher the latter be wide or up top. I also think Bannan's form makes him an automatic choice right now. And lastly Petrov, as captain and the nearest thing we have to a DCM, will start.
So you start with our usual defence and Given behind them and Petrov infront. Bent up top and then Bannan and Gabby somewhere in the midfield/forward area. That leaves two places and I think Jenas hasn't come not to play, plus he'd add some experience and strength to the central midfield area, so he slots in alongside Petrov. That last player is therefore from the options of Heskey, Delph, Ireland, N'Zogbia or Albrighton. I think ideally you'd want N'Zogbia in form and playing - again we didn't pay £10m not to play him.
So if that's the best 11, then foramtion wise it strongly leans towards 4-3-3 for me. Gabby and N'Zog wide of Bent and Bannan as the furthest forward of a 3 man midfield:-
Given
Hutton
Dunne
Collins
Warnock
Petrov
Jenas
Bannan
Gabby
N'Zogbia
Bent