personally my best command decision was organising my armies into "roman" style armies (pre-marius of course) - 4 hastati, 4 princepes, 4 triarii, 2 archers, 4 cavalry, general and peice of assorted artillary. It might not sound like a "command decision" as such but in battle, its incredibly flexible and a lot of fun. CA weren't lying about proper roman type armies being more useful ;)