These Big Guy'z have larges surfaces of flesh, perfect to begin with an airbrush. I invest in a common airbush from Prince August range (AM01) and it's a really great tool to paint miniatures. I admit that the "Pchit" effect is strong but on a magic flesh I think it's not disgracious.
Most of them are sculpted by Ali Morrison. His interpretation is less pulled toward the stupid monster like the C20 Troll of the Perry twins. Anyway I like both styles :)
Other important monster for Chaos army is the Chimera. In 3rd ed that monster is totaly created with random profiles, heads and tails. It's the most fearsome Chaos children.
Unfortunately, the Citadel Chaos Chimeras CM1 is ridiculous compared to his profil (but his position is interesting) . With regret I choose to paint Ral Partha - 11-414 Chimera (Ad&d). his body is more massive and I was able to use my airbrush to paint wings.