Forts and watch towers work well in combination at choke points. I personally don't like to fight from inside the actual fort, but I do like to put stacks without a general in there while a watch tower warns me of the approach of an enemy, at which point I can pop them out and plug up the choke point. If the location is just right you can even pull out only some of your units (To minimize the risk of rebellion), place them one space in front of the fort, and leave the rest of your men to be called as reinforcements.

It's best not to fight out of forts mostly because they negate any advantage you might get in terrain, seeing as they almost exclusively wind up planted in the middle of a wide valley or plain on the battle map no matter where they appear to be on the campaign map.