I have been a tube guy for a couple of decades but after demoing and then moving to Spectron amps - from stereo to mono block there can never be any doubt I made an improvement in my enjoyment of my rig. Now, there are lots of good SS, Tube and class D amps and similarly lots of overpriced but well hyped but not great gear. For me the bottom line was that the Spectron class D amps removed a veil that my previous tube amps had and also class D amps seem to have the speed and cadence to ensure that all of the signal reaches the speakers at the right time. Hard to define but easier to hear.
There are a bunch of great amps that I would be delighted to have in my system (assuming appropriate synergies) and I could name a short list of SS, Tube and Class D. My point is that circuit design, good board topography, effective procurement and manufacturing can deliver a great product, or not, so the best class D will sound superb and the poorly designed class D will sound like crap and the same goes for tubes, SS etc. etc.
Bel Canto, Rowland, Spectron are all great products.
My rant ends with the principle that system synergy ends up defining the quality of final sound - and most likely a product of electro-mechanical parameters.