It’s probably going to be a Reaver for a while (or some other Warrior with a decent DPS and survivability. Atm a Reaver seems to be the ace). But eventually people will max their manifests and get all the AAA-equipment and promote hundreds if not thousands of times. With all those extra attribute points* and cheesy gear, the best DW Rogue (an Assassin maybe?) will be able to dish out some ridiculous / broken single target DPS that everything else becomes pretty irrelevant.
*Even if you couldn’t upgrade attributes related directly to DMG / attack (Dex/Str/Mag), as it seems now, but still I can see that the best DPS monster will benefit most from all that extra HPs and Stamina, not forgetting Cunning which will benefit Rogues most if anything.
To be sure, especially if Cunning still effects Critical Hit Damage and there are any "craftables" which allow stacking of Critical Hit Chance, I could see Assassin or DPS focused Reaver, being highly played kits. I will stick with mages for starters, cuz ya know... Elves... and Magic... Ancient Lost Culture and Stuff... So, Cuz Lore-sons?