The Hold Guard could be interesting just for thinking up interesting ways of getting all the hold guard armor without straight up murdering anyone. Except maybe to get the winterhold sheild.
I'm leaning towards the Cryptstalker though. It's been a long time since i've done either the theives guild or dark brotherhood. Plus it has a list of in character reasons of why it would do the dlc's and faction questlines. The thing about the Cryptstalker is that i'm not sure what equipment i would use, or what magic/health/stamina ratio i should go with every certain amount of levels.