The best I've heard is an amp that was built, in believe, in the late 1930's to early 1940s. I don't remember the details, but, it probably was a Western Electric. Each amp filled a large vertical rack. I was told that good working copies go for something like $60,000 each. This was a very dynamic, lively sounding amp.
I also liked the pair of Audionote (uk) Sogon amps. These were also quite lively and had a really nice, extended, top end. To me, they sounded better on top than the Audiononte Gaku-On, though if one is looking for a warmer sound, the Gaku-On would be it.
I have not heard a lot of the solid state contenders in systems I know very well. But, I've heard nice sound from systems with Dartzeel amps and the Soulution amps.