Spikes under the Subwoofer?

What kind of flooring do you have? Is your system on the 2nd floor?

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.

spikes quicken the low frequencies,no typical bass overhang. Used in cases where a carpet is beneath the sub.
Each has individual characteristic. Same goes with those sorbothane that audioquest employs. However try out Foculpods which is cleaner sounding than Audioquest. The rule is "to hear is to believe". Note too that it has a relative weight which it is effective.So check the weight of the sub which is coupled to it.

There was a rickety old man in a rickety old wooden house with old wooden floors and a [chuckle] downward firing sub; Then there was a man with nice, solid concrete floors and a forward-firing sub; If you are into home theatre/audio, have a good, long think...before you decide where you are going to live.