Very true Celt. More siege equipment is always better. I just prefer to attack after only a one turn wait or at most two turns. But if you've got a large army, by all means, build as much equipment as you can. On a related note some may be wondering why a person shouldn't just bring a couple Onagers along. The answer is that while Onagers can be quite useful, they take a bit of teching up to get them. When you can get them however they'll come in handy. Even though they slow your armies Movement Points, the ability to attack instantly offsets that. In addition they provide a useful extra level to field engagements. (Onagers outrange archers by a good bit) A good buy for any general!

Your post leads me to another point as well. Never attempt to attack a unit on the ground with a melee unit you have on the wall. Your men will straggle out slowly in ones and twos, run around seemingly randomly while they attempt to form up, etc... In short even if your troops are significantly better you will be massacred. If you need to get off the wall, you must first find a clear area where your men can get down and form up at their leisure. Also, when attempting to move thru city streets, change your formation to the approximant width of the street. This will help to ensure that they avoid those frustrating tendencies to face odd directions of their own volition or run in what seems to be a random direction before following an order to move somewhere, etc...