If you unlock the best equipments, sure you can make them the strongest KO. There should be an option releasing them 'for teaching their secrets' or something. To do this, capture a unique spawn and talk with them while they are your prisoner. Truly strong equipment should be unlocked by you. At first they only have access to somewhat powerful armor. Under player's command every KO that's above average can work. For heavy cavalry I used Dawn even though there are better heavy cav KOs reminder this was before their level is reduced to 40 from 50, don't know if this is a nerf for skills or buff for lower wages. To be honest, you don't have to choose the best of the best. Still, many late game armor can outmatch even the best KO armor so you can just not care about armor either and go for the looks. You can join them for free, high quality armor. However Knights of KOs give you their armor as you level up in their ranks. In some occasions you get free troops of that KO but eh, it's not enough to make a difference in my opinion.

If you want their troops, you don't really need to join them. Meaning, having highly skilled companions, a walled settlement and enough money for equipment upgrades. I have around k denars, is it a good time to take this direction? As soon as possible. My weekly expenses always comes up around k, so I have to grind some tournaments in order to not fuck my budget up. Currently I'm a vassal for Ravenstern, roaming around Pendor with a army 40 expensive Hero Adventurers, and othersI own Ravenstern city, a castle and another village.

Prophesy of pendor mercenary company