On, because with the grilles off, they're ugly. I'll gladly sacrifice that last 10th of reproductive quality so that I'm not looking at a speaker thinking, "Boy, that's ugly."
Grills ON or Grills OFF?
With my Signature S2s, I prefer to listen with the grills on. Even though the highs are ever so slightly rolled off (which, with this speaker is not necessarily a bad thing), the dispersion and the ability of the speakers to disappear is better. Plus, I like the protection factor. How do you conduct your listening sessions, and why?