http://www.dakkadakka.com/dakkaforum/posts/list/297729.page
The last time we did this, it went Khorne, Tzeentch, Nurgle, Slaanesh. Which kind of surprised me. I expected Tzeentch to be last. Personally, I vote Nurgle. Sure, you're just as f-ed up as you would be with any of the others, but A) I think you have a longer lifespan, and there seems to be less in-fighting amongst Nurgle's brood. B) Nurgle has the decency to make you insane in such a way that you view your hideously rotting meat-suit as enjoyable, but not to the point that you can't focus on other things.