It always depends on the factional strenght, but I tend to prefer ranged power.

For example as the English, I have 3-4 longbowmen, to attack the enemy backed up by spears, and later armoured swordsman, and use calvery to harrass the enemies archers. Later as seige and gunpowder come along, I add a few seige units to project power further.

This forces the enemy to attack you or lets your archers to wipe them out. Generally I play defensively, I let the enemy attack me by seiging their castles, or holding bridges.

The key to my armies is to minimise casualties, so generally my main casualties are in calvery which are easier to rush up to replace. As the English I can get away with smaller armies, knowing that I will suffer few casualties.

If playing an Italian faction, my armies are based on pavise crossbowmen and Italian Spear Miltia backed up by Calvery Miltia. This leaves me fairly weak against heavily armoured units, but due to the incredibly cheap to maintain armies I can have more armies and more units readily availible to meet any threat. So I will suffer slightly more casualties but they are cheap and very easy to replace. Italian armies are all about economy, plus with the key cities so close its very easy to reinforce.

Stonewall