There has to be an argument for Dusknoir, and I guess it's up to me.
Obviously Dusclops is superior regarding bulk, but its attack is pitiful at best, reducing it to using to using either night shade or seismic toss for producing reliable damage outside of status, allowing normal and ghost types respectively to be able to switch in with relatively little worry.
This is where dusknoir comes in. Dusknoir's decent base 100 atk along with its great movepool allow it to be a great offensive threat. With STAB priority in shadow sneak, the always useful earthquake, shadow punch, brick break, the elemental punches and a wide variety of support moves Dusknoir can be a good tank, support Pokemon, or even a major offensive presence in trick room, reflecting its versitality, especially compared to the relatively one-dimensional dusclops.
It should also be noted that Dusknoir still has base 135 defenses, which still makes it quite bulky, and that dusclops and dusknoir practically share a movepool, though with bulk and offensive presence, dusknoir can take advantage of more of it.
Hope this helped.