Don't play Grey Knights, especially if the other player is a
TFG
Daemons are a decentish army, but suffer from the problem of having to split their force and roll randomly to see which half you get to deploy.
I try to make each half a capable mini-army, so that either way i have something i can use.
If i take 2 soul grinders, or daemon princes (etc) i will put one in each half.