The "best" commander depends on the type of troops you are using and the type of troops you will be fighting, as well as whether you are attacking or defending.

Basically t2 commanders of the type of troop you are using are best used to attack.  For example, t2 cavalry commanders leading cavalry, t2 infantry commanders leading infantry, etc.  So human knights leading human cavalry, dwarven stalwarts leading dwarven infantry, elven trueshots leading elven bows and orc ... well, orcs should not attack with spears, but if they do I would think they might be the exception and use cavalry commanders, at least for NPC hunting.  Orcs, please tell me if I'm being naive here.

In terms of defense, you want to use a t1 commander of the type of troop you will be defending AGAINST.  Since most often you will be defending against cavalry unless you are fighting dwarves, usually you will want to have at least one t1 cavalry commander in any city with substantial defensive troops.  If you live in a dwarf-infested area, you might consider having a t1 infantry commander.

I like Homunculus people ..  

Thanks for the info