I believe Nanderson is on the money in the context of most reasonably priced subs. Personally, I prefer the use of spikes with subs, BUT - there can be an issue with downward firing subs in that the space under them is affected by the insertion of spikes, AND if cabinet resonances are significant then Vibrapods are very effective. I agree with Nanderson that the beneficial effect of Vibrapods is to remove cabinet resonance, but there is a downside too in that energy is not released quickly - although some may like this effect because it will add perceived bass weight. So if the sub is a bit suspect in the resonance area, use Vibrapods. If cabinet resonance is not an issue, use spikes. If the sub is downward-firing, be careful to maintain the manufacturers intended clearance from the floor.
