In addition to taking down the gate, I use artillery to knock two large holes in the wall on either side of the gatehouse. For the main assault, I send in halfway-decent infantry along with whatever scrap/leftover units are at my disposal -- I often use mercs for this as well. I only send in heavy infantry/elite units to back them up if it's *absolutely* necessary.

Quote Originally Posted by The Darkhorn
This is why I never autocalc assaults. I want to take the casualties out of certain units. When I autocalc, there seems to be no rhyme or reason to it with nearly every unit losing a few men.
Agreed. I often manually fight castle assaults for the specific purpose of ensuring that my crappier/leftover units bear the brunt of the casualties -- it drives me nuts to auto-calc a castle assault, only to discover that my knights and archers had an attack of the "stupids" and apparently decided to join the infantry in the battle.