Last time I completely wrecked them with my guys attacking at night and using spears and pikes (but, to be honest, I was able to kill almost everything with that setup). Another way of killing them is having good archers/crossbowmen who will snipe them out and then snipe out any non-shield goblin until you run out of ammo. Any survivors can be moped up with your melee fighters without much trouble.
But I wouldn’t recommend attacking them until you get at least a few levels and some decent gear.
