Which of the Warlock creatures do you like the most?

And in what way are they casters? Besides the Djinns (and even they are only random casters), none of the aforementioned units are casters.

Nazg, there's been a mistake ;) Dryads are indeed casters. Or do you not remember how much trouble they can cause with "Wasp Swarm"? I agree about the rest; they don't seem to be able to cast spells, unless you consider their activated abilities as such.