With all the heavy weapon upgrades and the heavy weapon ammo boost armour piece, Cain has 2 shots and the Collector particle beam has 1000. I generally use the particle beam when facing down Collectors, Harbinger and the Praetorians (the floaty boss at the end of Horizion) get absolutley shredded by it.
But I like Cain the most. When in doubt, nuke the s**t out of it.