Feudal Seargeants:-

Charge 5 Attack 0 Defence –1 Armour 1 Speed 6, 10, 11 Morale 2 Cost 200 Support cost 62


Armoured Spearmen:-

Charge 5 Attack -1 Defence 2 Armour 3 Speed 6, 10, 11 Morale 0 Cost 250 Support cost 50

As you can see Feudal seargeants cost 50 less but require 12 more upkeep per turn. They have rubbish attack but not as bad as the Armoured guys. But The Armored guys have Higher defence and Higher Armour. However the morale is better for the Feudal Seargeants. Just depends what you prefer really. However:-

Rus Spearmen

Charge 5 Attack 0 Defence 2 Armour 3 Speed 6, 10, 11 Morale 2 Cost 325 Support cost 62

These seem to be a mix of the best traits of both (if you can get them that is ;) ). More expensive but definately worth it.

[Data taken from the Unit Guide by frogbeastegg]