Some use Boston Audio graphit with steel inserts tuneblocks made specifically for spiked speakers with great results. Where are you? You are on a quest to find the thing that works best. You could also experiment with various spikes and footers of different materials, weight, shape; and with three or four footers.
Vibrapods to Preludes
After spiking speakers seemingly since first supporting stereo stuff self seriously, I've succumbed to a set of Vibrapods under Silverlines. It defies logic and makes me realize that maybe everything I know is wrong but damn, it works swimmingly. Sweeter mids, wider and more stable soundstage, etc. Go figure...who knew? Where am I?