Was tempted with Hashut but in the end I had to go with Slaanesh. Not because I'm a pervert (really more in spite of it), but because what Slaanesh represents is something that I think is really sinister. The pursuit of pleasure, excess, perfection, pride, etc. All those things are good in varying small doses, but the veteran Slaanesh devotee never quite achieves the pleasure they want, they're always seeking, craving for more, as their mind becomes resistant to even the most extreme and debased pursuits, they really live in a state of frenzied anguish, trying to scratch an itch that won't go away. To sate a hunger than won't be sated. To satisfy a lust that won't be satisfied!
Plus the whole idea is pretty much just the Cenobytes from Hellraiser. Angels to some, demons to others. Pain, pleasure; all the same!