Most musical, enjoyable affordable amplifier

The most enjoyable listening , out of scores of amps, tube and ss, I have ever enjoyed, is the humble little Dynaco ST-35 with Mullard el-84's, and a Pass First Watt F6 clone  built from Pass article ,and DIY Audio web site.
Class A does it for me.

One of my favorite amps was the little PSE Studio IV. Compared to just about any other amp near it's price, whether driving my Vandi 2Cs or Quads, it was like pulling back a veil and just hearing the music...Jim

I bought a modern single ended tube "boutique" guitar amp (I'd owned old Fender amps, some of which were single ended) and liked it a lot, and it got me wondering what single ended tube hifi would sound like after many SS amps over decades, although at the time I was enjoying a push-pull tube power amp in the rig. I read about Dennis Had and watched an interview with him on Youtube that I liked, and a slightly used Firebottle amp showed up on Ebay. After a year or so I'm still smitten, and while using it with efficient speakers and a tube preamp it simply works for me as it sounds astonishingly good. Seems to be a keeper.

First Watt F7, XA60.8’s, Accustic Arts Power ES, NAD m22 - none perfect, but all pretty musical amplifiers I currently own.  Two that I currently own but a little disappointed with from a musicality standpoint: Leben CS300 is a little too flabby (although headphone section is satisfying), Krell Evolution (a bit too analytical and thin, but has some wow factor areas as well).

That being said, I think the DAC section is the starting point of the conversation.  Preamps are fun to compare and contrast as well.