If there is any chance or reason that my enemies will be in clusters of 2 or more (practically anytime, maybe not rumble as much) I go all out as void. 3 guardians in a cramped hallway? Novabomb! Guardians at the heavy? Novabomb!! Rampaging hammer-bro, Raiden or bladedancer threatening your team? Might actually cause multiple fatalities? Novabomb!..while screaming like a little girl because that shit always make me say "oh shit shit shit" when they come around the corner. But that's my opinion, I play void more than the other sub classes because it fits my style best. Just have to mess around on all of them to find your comfort zone.