I assume efficient means that the damage done by the figure and the support provided by the figure to allow teammembers to damage is high relative to the figure's points.

I would go with:
Deathstroke (any version)
a clear winner in my opinion

Other DC figures that immediately come to mind:
Nightwing
Green Arrow
Green Lantern (all of the Hal versions are very good)
Wildfire (causes considerable ranged damage)
Cyborg
Mr. Freeze