Personally I would rather have a chisel type of head to shatter bone some before the blades and the rest of the arrowgets there. Provides a more open path through a bone, like a shoulder blade, for the arrow to followthan a COC head will.

Having said that, if you are pulling low enough poundage then neither one will get far though a shoulder and the COC will give easier penetration through soft tissue between the rib cage.