They each have a different focus. Two handed excels at single-target damage, and will easily surpass dual wield in that regard. Nothing dual wield has can compare to even basic wrecking blow spam.
Dual wield, on the other hand, is the king of AoE damage among melee characters. Two handed can survive more damage in aoe situations, but dual wield stomps all over 2h for aoe damage output.
At the moment, my nightblade uses both - 2h for single target, dual wield on the second bar for multi-target/aoe.