Over the years, I have tried various spikes from the simple ramset spikes that come with Sound Anchor stands to Audio Points and then to edenSound's Bearpaws with spikes. In the past year or so, I switched to using Herbie's Giant Fat Gliders and then to springs under my main speakers (180 lbs each with stands) and two subs (150 lbs each with stands). I was able to purchase individual springs and damp them with loosely applied thin heatshrink and therefore did not have to purchase the more expensive Townshend products.
The springs work great and offer the benefits described by other posters over spikes, at least to my ears. My main speakers roll off below 40Hz so I recently tried going back to the Herbies Giant Fat Gliders and I do not perceive any noticeable sonic difference between the gliders and the springs. I do plan to keep the springs under my subs where I believe they offer the most benefit. I am also using appropriately sized and damped springs under some of my electrical components and find them to be effective and preferable to Stillpoints.