Did you have something specific in mind?
Yes, my experience rolling one type against the other was in a Mesa Baron (tri-tube) amp. There I found the KT88's to be a bit too hard and clean for my tastes, giving the Baron an almost SS sond to it. I longed for something a bit more warm in comparison. At the suggestion of a few folks (Jon at the Tube Store, and the tech guy at Mesa among them), I tried 6550's instead...I think they were Svets, but it's been a while...maybe in a previous post of mine...anyway, sure enough, in that amp and system, and to my ears, the 6550's sounded warmer and had a wonderful midrange, with a bit of sacrafice to the bass. On that amp the bass compromise was no problem as it is a prodigious performer there. The tubes were Svet's in both cases as I recall. This is over five years ago I think, so details are open to correction, but the overall impression is quite accurate, I'm sure.
Marco