Vibration isolation or absorption?

Like almost everything involving vibration damping/control, it is a matter of tuning, so there is no definitive answer.  I've tried various speakers on damping platforms (the entire bottom of the speaker is in contact with a platform designed to transfer vibrations to the platform where the energy is dissipated as heat) and also tried the same speaker with spikes designed to transfer that energy to the floor.  In some instances damping the energy sounds better (tighter bass), in others, transfer to the floor sounds better (excessive damping can make some speakers sound lean or "dry" sounding).  It is really a matter of trial and error and personal taste.

Generally speaking, if you have a suspended wooden floor, and the bass sounds a bit boomy or muddy, decoupling from the floor would help.  If you couple with spikes, vibration is transferred from the speaker to the floor which acts as a sounding board that may make this energy more pronounced (and also delayed in time).  

What works best for any one person depends on so many factors that I find the best advice is to try different approaches.

As I stated before, vibration control is a matter of tuning.  Not only does the approach matter, but also the degree of vibration damping or transfer that matters.  I attended a demonstration of Symposium platforms that all work in the same way, but differ in the amount of damping provided.  On one particular component, a CD player, the shelves made a big difference in the sound.  But, when the most expensive platform with the highest degree of damping was put under the CD player, the sound became too dry and analytical.  This was not just my conclusion, but everyone else thought the same, including the Symposium representative.  The idea that the "ideal" is the least amount of vibrational energy is not always the case and this goes with all components as well as room treatments. 

The worst room I ever heard was one designed and implemented by Corning that maximized absorption of sound hitting the walls and ceiling--this room was so unlistenable.  I've experimented with applying extra damping to the outside of speaker cabinets and in most cases the sound got worse--the designer probably tuned the sound using such cabinet vibration.  

I recommend trying different products. but keep and open mind and be willing to accept that the new product may not offer the right kind of tuning or the right degree of tuning.