KoTD is pretty badass. And you can get a fair few if you deal with the Red brotherhood on a regular basis.
On the other hand, if you join their respective orders, they are about equally easy to get, and you can get them in pretty large numbers.
That is, you join the order, and do the gather 200 renown quest with minimal losses, and recruit form the survivors.
If you have a high surgery skill (10+4), and a good tactics skill, you can expect to complete the quest with <70% of your starting troops, if you do many medium difficulty encounters. If you go hunt a minor faction army, you're probably gonna take more losses. It's a good way to get quifgens quest out of the way though. Jatu ain't so tough when they have to charge into a wall of Wyverns (or Immortals).