Most of my stacks (untill i can get cannons) are :-

6 units of Armored Swordsmen (fully upgraded from citadel with swordsmith guild)
5 units of Retinue Archers (fully upgrade ive also got headquaters for woodsman guild)
4 units of Hospitilar knights (fully upgraded, i can get templar no matter what i do)
1 Generals bodyguard (upgraded)
4 Spearmen (fully upgraded from a citadel with swordsmith guild)

Thats the sort of offensive stack i use it works out roughly at around 2000 men (on huge armies) and with that type of stack ive managed take out multiple stacks of around 5000 units in total with roughly 70% to 80% of my men still alive after the battle.

I would actually use dismounted english knights but there bugged really badly (2 handed weapon bug) so i just stick with the armoured swordsmen as they do brilliantly for me.