Well it isn't really a fair question. Assassin will obviously deal the most damage but it also takes the most time and patience being sneaky and if you are ambushed by multiples you instantly lose that immense damage. Two Handed and Dual wield can be categorized together, either you beast out on pure damage with the two handed or speed with the dual wield to get damage off quickly. But people are forgetting exploiting weaknesses. For example only dual weild or one handed can really do this as it requires elements. With dual you can enchant one fire one frost and damage enemy weaknesses. But with one handed you get a free hand for a massive selection of spells that can exploit all weaknesses buff and protect you or simply conjur others to fight for you...
except all the spells suck late game versus how high the weps scale. If u wanted to increase dmg even higher using magicish stuff (but why) you could lay on element dmg enchants on 2hander and then get the destruction talents to increase those areas of damage.
And to whoever responded about assassins backstab like i said. Ya you can get higher dmg obvy with 30X daggers but wtf is the point when u can 1 shot everything without sneaking. And to the bow glitcher this game is to easy within the un glitched crafting mechanincs if u 1 shot with a million glitched or a 3k not glitched who cares if its a million?