I have been playing since the MTW2 came out in November, and I must say I completely disagree. Most battles are not sieges, in fact you can usually avoid city fighting if you just wait it out. If you want to guarantee a field battle, appear to have a weak stack in your enemies territory; or attack your opponents wherever the mood strikes.

But if you want to have successful city battles, DO NOT USE CAVALRY! Use your heavy troopers to wade into your opponents, put your archers on the walls, and use spear/pike troops against the enemy cavalry. Also, put 2 or more spies into any settlement that you wish to be your own and look at what the percentage is for the gates to automatically open when you approach. If this number is not 100% or better, put another spy into the city. I rarely use artillery to get into cities, because I have to pay for the repairs after I take the city.