To answer your question a sniper head shot would kill them in one shot. A body shot rocket launcher and also kill them in one shot. Also shotgun melee the warlock will also kill them before they can kill you, but it will only work if you run away first and try to bait him to chase you. Then shotth melee will kill him once you're close enough to him. Also a golden gun can oneshot them, the heavy fusiom rifle can kill them in one go as well. Umm the high impact heavy machine guns can kill them in 5 shots to the head also. The hunters shadow shot will completely shut then down if you can bait them into he trap. Also smoke and vortex grenade can also kill them as long as you are using envenom. Umm 2 fusion rifle burst will kill them as well.. Theres pretty much alot of way to kill them as you can see. Just use your head and be creative.