Crit Disclaimer:
If you're gonna run crit at all, run [Primed Ravage] with Arcane Avenger + [Combat Discipline]. This weapon's base critical chance is still too low to be worth using a mod slot on crit chance. It's probably still better to run a Primed Cleanse mod instead though.
We run Heat x3 because we want Heat to be weighted the highest, and Heat proc damage is based off of the total Heat % of the weapon that inflicts the first proc. If you replace any mod for [Primed Ravage] I'd say swap Armaments for it.
Corrosive vs Viral really doesn't matter. As far as I could tell there's no difference up to lv300 enemies and I don't care to test it further. If you shoot a guy he will die, use Viral instead if you want.