Seeing as the dreads have no ranged weaponry I would suggest Khorne. However, depending on the amount of Berzerkers you have it may look odd having two dreads and only one squad to go with them. Personally, I would do them Death Guard unless you have a sizable amount of Berzerkers to make it look proportionate army wise.
Then again I may have thought entirely too much about this and just do what looks cool. One of each would allow you to have fun with two schemes and will keep the painting interesting for you.