In the attack, you want your best attacking general on one of the wings. The attack really needs to start there because one side of that army is guarded by map edge.

But the center position is absolutely crucial for the reasons elmo says. In games between 2 very good sides, the reaction and support given by center usually will tip the scales. Center need not be the best attack general, but must be the general with best anticipation and support.

--- Amp the troop pick is critical... but amongst good players they all pick good and so it then comes down to ability.