I am pretty much always alone on this, but my favorite setup for a warlock in a WG squad in a serpent is Destructor. Conceal is the "duh" power for footsloggers, combined with fortune it's all sorts of fun, and most seem to think that Conceal is always the right choice. But mechanized, in a tourney army, I always have destructor, as it allows the option of going after a larger squad of cheaper stuff if it becomes necessary. That unit is too many points to have sitting in a corner when there aren't any optimal targets, I like having a decent second choice, especially since I usually have 2 serpent squads in my lists.