Probably referring to Spike Traps > Scatter. A LOT of burst damage quick - pretty much more than anything else for its cost.
Cluster Arrow I'm not sure as it's hugely restricted by the Hatred cost. I've speculated that if you had enough regen and some gear that reduced it's cost, it would be pretty godly though. As it stands, you could get maybe 3-4 shots off before running out of Hatred (unless you had uber gear tailored for it), and even though those shots are very powerful, targeted AoE and single target damage, you're pretty much out of firepower until you regen more Hatred.
Cluster Arrow->cluster bombs is amazing damage. I ran it pre inferno. Problem is you pretty much have to go attack speed, bomb build to generate enough hatred which isn't viable in inferno.