Depends on what you mean by powerful... If damage-wise, then definitely Assassin's strike. I get around 1,600 damage with an epic critical. That doesn't include the bleeding either. Then again, mojo reaver is pretty great. My epic hit is around 1,500 (on a musket, medium will). However it's not as strong since it leaves no DoT. Defense-wise, Valor's fortress is the best. It takes off 50% of ANY incoming damage. Zeena's fire bugging you? Here's that problem solved! Sure, it's only for five rounds but if you're being attacked non stop then it's great. Buff-wise, Battle Zeal has to be the best. 50% accuracy and dodge, an amazing combo. With it my swashbuckler's dodge goes from 151 to 227! It's an amazing power to have, it makes even a musketeers dodge a force to be reckoned with, triggering their return fire (if emmett who comes with it by default or even zeena).