I think it depends on the spares you have available, but I also used a spare Berzerker for mine.
I used the legs, body and head from the Berzerker kit, but one of the bigger fancier power plants from from the Possessed set.
I then used the chainsword arms from the Raptor kit as they are a better mould and look more dynamic.
It has made a dynamic looking model charging forward who can throw out nearly as many attacks as a full squad of pitiful loyalist Marines