For me a good commander is one that chooses the battle on HIS terms and chooses the best course of action for different scenarios,and who never retreats,being constantly aggressive and persistent,harrassing the enemy until they either tire or are destroyed.Another useful trait is a commander that is able to think on his feet and adapt to changing circumstances and is able to adopt new tactics to deal with that.
In a nutshell - initiative,spacial awareness,aggression,persistence,adaptability
