With all the resurrection of gut strings and development of new hybrids, such as Velvet, Genssler et al. and the recent trend of rediscovering spiros, I've come to this personal conclusion based on my two basses: Gut strings and the "hybrids" (Velvets etc) seems to compliment basses with a sonically "simple" profile such as Juzeks and plywoods. They bring out punch and warmth, as well as a nice "acoustic" reproduction thru an amp. Spiros seem on the other hand to work well with sonically "rich" basses, giving them focus and punch. Comments are welcome!