The way the guards at Solitude talk about her, I imagine Solitude's court wizard would make one ruthless follower.
Babette for the creepiness of it.
Neloth for the intellectual stimulation. He follows you for that one quest and hand's down, it's my favorite quest in Dragonborn.
Katria, intellectual and a good warrior. I always miss when I finish Lost to the Ages.
Agree, Sinding would be pretty sweet.