IMHO, you need to be able to field different types of troops based on your opponents. I've always started my kingdom by taking Halmar which means that I'm at war against the Khergits. I will assault Halmar using Nord Veteran archers and Nord Huscarls which I had trained up beforehand by being a mercenary for the Nords. After I take Halmar, I will leave the Nord Veteran Archers and Huscarls as garrison. Then I quickly go around and try to recruit as many watchmen, caravan guards, mercenary horsemen and mercenary cavalry as I can sometimes having to sneak into other Khergit towns to recruit at the tavern. With training, the watchmen get upgraded to caravan guards, the caravan guards to mercenary horsemen and the mercenary horsemen to mercenary cavalry. I choose an entirely cavalry based army for field battles because the Khergits are cavalry based. Foot solders don't do well against mounted archers because the mounted archers tend to run circles around foot solders, shooting jarids and arrows. With a cavalry army I can run down and destroy Khergit war parties. Additionally, the Sarranids tend to decalre war on me as well. Sometimes Swadia also joins in. I choose mercenary cavalry because I won't incur any morale penalties as opposed to using Mamlukes, Swadian Knights or Khergit Lancers if their faction is at war with me. So you need to first think about what factions you will be going to war with and adjust your field army accordingly.