Depends on the circuit they're in. In my JA80s, the KT90s were thinner harmonically, brighter and lacked the dimensionality of NOS KT88s; punch was about the same, although the brighter sound of the KT90s made the high-frequency leading edge of transients seem a little "crisper". The 90s seemed cleaner sounding and more detailed at first, but got duller and more wearing quickly, while the Gold Lions have only gotten better and sound more "right" to me. Can't tell you how the new KT88s stack up, and keep in mind my amps are older and were designed around the KT88s; newer designs from Jadis, such as the JA 100, 250 and 800s and Orchestra Reference, were designed to work best with the KT90s.
