Well, I think it would really depend on what group of Chaos you use. If it's nurgle, I definately would choose the Pig Iron stuff over the Wargames Factory. I've got some of the Wargames Factory minis and I think they are great, and they come with a nice variety of heads, some more Chaos-Looking than others. The "fun extra" head is looks like a Mindflayer from D&D.
Check them out here
http://wargamesfactory.com/wargames-factory-store/shock-troops-sci-fi-greatcoat-troopers
For variety and ease of use, the Wargames Factory stuff is pretty nice, as they are relatively cheap, and are plastic. One thing to consider is that they do not come with bases, so you'll have to go to a bitz website to buy them cheap.
The Pig Iron stuff is very nice though. I'd use them for Nurgle or just plain corrupted, neglected guard.
Hope this helps.