Question on garrisons

I usually use Town Watch to garrison a city, as they would seem pretty competent if the town actually came under siege by the enemy. Are peasants better? How many units to you guys use as standard?

I'm trying to figure out how I can keep a single attack force, without having to build an army, get it all assembled, then attack one territory with it, but I have to leave the army there to keep the city from revolting. Then I go through the whole process again. It's quite painful. I always choose to exterminate the population.

Any thoughts?

Town Watch are definitely better than peasants. If you're using them alone to hold a border town, watch out! It's likely they will lose it all by themselves.

However, if you've got a nice seige army built up raiding provinces, then you can move that army in and out of settlements as needed for raids, and leave town watch to keep the city from revolting for a turn or three.

Also that will take care of the build/crush/build/crush cycle. Take the time to build up two tough armies, make sure they've got a steady (but not torrential) flow of reinforcements, and go province-hunting with them! When you've got a town, you've still got one army outside to parry off reprisals, you can build town watch, and then take your army (with the trickle of new recruits) off to conquer elsewhere.

In terms of preventing a revolt do stronger units serve as a better garrison? For instance if I use Hastati instead of town watch will I need less units to garrison the town?

I'm pretty sure unit size is the only factor when it comes to town order. Peasants would be the best choice if you're not concerned about weathering a siege.

It was unit size only in Medieval, and i don't see why it would have changed.

I'm not sure that it is town size. It might have some modifier since I don't see that a unit of barbarian peasants has helped me more than lets say a unit of axemen.