Depends on the boss. I carefully tested with Warpriest, eliminating variables and doing it more than once, methodically recording results. The highest DPS weapon for that encounter is Touch of Malice + Weapons of Light. However, it takes practice for five people to share one bubble. The second highest DPS is Sleeper, plus a high impact legendary sniper for when you are out of heavy ammo. Black Spindle + machine gun can't match either (30% below Sleeper, which is 30% below ToM at its best). But 1 - Who cares, Warpriest is easy to kill. And Spindle works well for Golgoroth too. And special ammo drops more often than heavy ammo. Personally, I use Spindle. 2 - This is specific to Warpriest and may not apply to other encounters, for various reasons, most importantly the length of time you have to shoot.