Not 100% certain on things nowadays, but the following is my impression and it's probably right:

In terms of pure agro: Steel Cyclone > Overpower > Flash

Flash and Steel Cyclone both are circle effects centered on you. Great for using while moving. Or when you need that agro *NOW* for a new add. Or when there are targets both in front and behind you. (Compared to Overpower where you have to target and face)

Flash gives you something to do while under pacification from Berserk, or when out of TP.

Overpower is like the "bread n butter" area attack though: repeatable damage & agro. I like going Berserk + Bloodbath + overpower spam. Mix in a Steel Cyclone or Unchained perhaps.

Also, when agro'ing newly spawned adds and positioning them, I like to go Tomahawk then Overpower because Overpower has a longer range than melee and relatively high agro amount (way better than a 2nd Tomahawk). Example: Dancers in t7.

And for those who said Steel Cyclone is free... it costs you a crit buff and the opportunity to use Inner Beast/Unchained. A cost worth paying perhaps, but not free.