I prefer the rubber feet. They decouple the speakers from the floor. Also, they are far less hassle.
If you hear tremendous differences between USB cables (for example), you have golden ears and should try the spikes. Otherwise, just enjoy your speakers (and unmarred floors) the way they are.
If you hear tremendous differences between USB cables (for example), you have golden ears and should try the spikes. Otherwise, just enjoy your speakers (and unmarred floors) the way they are.