They go about it different but sort of result in the same thing. The goal is really to isolate the speaker from passing vibration to the floor or whatever they're connected to in the case of bookshelf speakers. Between rubber feet and racket balls, I'd say no difference. For floor standers, I prefer spikes for stability, but that isn't exactly compatible with wood (they sell ones with cups for the spikes),but in the end as I mentioned, the result is the same whichever you choose - isolate them from vibrating the floor.