Alls y'alls are crazy. It is never about a single gun; it's about a loadout of weapons. WILDFIRE has the best hull damage/energy drain ratio (other than Nomads which have 0 energy drain): 1075 hull damage for 220 energy (per shot). TDC has the best shield/second ratio: 4968 shield damage per second at a drain of 388/sec (12.804% effeciency). But if you can't handle class 9 weapons, Adv. Debilitator(class
,a Rapier(class 7), or Borroco(class 5) will do. There's no decent Class 6 shield-killer.
... there are so many stats you can compute with the weapons, it depends what you're looking for. The nomad weapons will have an effeciency (damage/drain) of 100% because they suck no juice. The Vulture 2 (class 5) is 2nd in hull damage effeciency: 6.192 (161 damage at 26 energy [3 shots/sec). Maximum hull damage belongs to Diamondbacks and Cerebrus (which have identical stats).
Heck - you can even break it down into damage against types of shields... you just have to match your loadout with your style of fighting. If you're a sucky shot and keep firing, you don't want a Cerebrus because it will drain your battery at 2 shots/second. Sunblast A (class 6) gives you 8 shots/second with 79 hull damage/shot at 19 energy drain. That's a possible 658.07 hulldamage/second draining 158.27 energy... and 8 chances a second to hit. The Nomad Blaster gives you 4 shots/second with a max possible 2540 hull damage/second - but zero energy drain...
...and I'm gonna kill, kill, kill, until the killing's done!