There is also the question of availability. I am sure, much people would like to bring more Hellions.
Then it depends on your strategy. Do you want to go massive on Incubi? Or more Wyches?
Some people use DT Chronos, Chronoi, Chronusses, well, whatever...
Take a look at this article!
There are so much different builds, you can go.
When I'm good, I'm very, very good. But when I'm bad I'm better.