Rip & Tear Mk II
 Zealot Build - Warhammer 40k: Darktide 

Ranged Weapon is mostly about preferences, I like the Zarona's fast 1 tap potential on gunners & specialists, the sprint speed and good ammo economy as long as you have access to a survivalist's aura.

The most efficient way to clear a horde is to loop H1 > L2, with the eventual push attack to create space. This packs enough stagger to handle anything up to a rager pack pretty effectively. Beware of Crushers & Maulers, for they do not give a flying duck about your L2, even to the dome, even with 5 stacks of Punishment...

Single target can be revved H1 spam to the weakspot for relative ease of use, or, if you have the execution for it, revved H2, accessible after a simple push (so drop the block before starting to buffer the heavy swing). 
It staggers anything short of a monstrosity (and even a beast of nurgle if you hit the WS), while dealing massive damage, especially on a charge.

You'll start reaching the sweetspot for damage and attack speed at 3-4 stacks of martyrdom. Further stacks are not that helpful, either you crit and 1 shot the crusher, or you don't and it'll take two revved heavies.

Last note : Attack speed is great for your horde clear, but it does not appear to fasten the tick rate of the revved attacks, so the only benefit you gain in single target damage is the faster revving up animation, which can be used as a cancel for the recovery of the previous revved heavy.