I know the Hive Fleet comes and eats everyone, I just like the Genestealers as a separate thing. It actually gives a legit alternative (which is why it is of course vorboten.) Be an individual who might succumb to any number of things or become part of a hive mind that consumes your identity?
Edit: I also have a fascination for Hiveminds, especially if it leaves individual personalities. It's either completely utopian or dystopian, never portrayed inbetween.