Everyone has their own playstyle. That being said each spec fills its individual niche.
The best advice i have would be to experiment with each playstyle and see what suits you most.
As for darkness , i dont see the dps comparison. Its also still relatively squishy.
Unless the object is to keep several people occupied while teammates perform their
Duties i cant see the merit in darkness in pvp.
Thats just my 2 cents. And for the record im 5/33/3 and i see 200-300k dmg per wz
In a decent pug.