I voted for bondage but humiliation came in a very very close second. Kat's comments on "less than human" made me ponder. On further thought, I think it's a vote between reality and fantasy.

In life, few things rival a helpless woman in bondage, unable to resist the evil plot to befall her. In fantasy, it is much more satisfying (for me anyways) to push boundaries, those of safe, sane and consensual. Hence it is much more fun to humiliate a sub - to treat her "less than human" and to push her against her will not only physically but mentally as well.

Having said that, I disagree that humiliation is equivalent than "less than human". In fact, it is "more than human" or at least, true to oneself. Different strokes for different folks?