Every player character in this game can be good or evil, can be powerful or OP, can be a killer or a murderer. However, "The Dark Urge" (its in-game full name) is not any of them. Otherwise, in terms of character build, what can possibly distinguish the Dark Urge from yet another evil Tav? You could just pick one or any OP build and play it as your own Dark Urge. There would be no such questions as asked by OP here. Which to pick would all be purely based on personal preferences.
However,
The Dark Urge per se is not an ordinary character, an ordinary killer or an ordinary murderer. It has the following story-wise unique traits:
- Murder people without being a murderer
- Highly skilled in deception and/or intimidation (and persuasion on rare occasions): if you succeed in making a kill, you can (always or almost) get away with it with no bad consequences on your own part.
- Make a kill solely for the sake of making a kill
- Durable in combat: if you fail to make a kill the way you have wanted, you can still get away with it any way you like. If you have to flee in order to avoid getting put down for your attempted murder, you are not Dark Urge enough.
- Has the raw power for making a kill with just a thought
- Barbarian's Rage, Bard's Inspiration, Paladin's Oath, Druid's Shapeshifting, etc. don't fit into the perceived nature of The Dark Urge very well: If you need a preparation for combat or a certain faith for combat abilities, you are not dark enough to be "The" Dark Urge.
Of the three builds you mentioned, only the Sorcerer (Storm+Tempest) build fits The Dark Urge perfectly, for the following reasons:
- Can be highly skilled in deception and intimidation
- Can be a very durable tank wearing heavy armory and holding a shield
- Can wipe floor with this game's most powerful damaging spell
There is a reason why the default in-game class for The Dark Urge is Sorcerer.
BTW, if you (being The Dark Urge) wish to hire Minthara, you should never choose to be a pawn of hers. If you choose to obey her command as a pawn, you should murder her in YOUR sleep later. This is the way of the Dark Urge. Otherwise, you would be no different from an ordinary Tav that chooses to accept both her order and her offer - in other words, you would be just an ordinary Tav who wishes to follow the steps of The Dark Urge but who doesn't understand The Dark Urge's true nature.
Regardless of being an evil or a good force, The Dark Urge is capable of getting every possible companion into the same party in a single playthrough. If urged to do so, it can murder any of the companions at a later time.