SET vs Class A vs tubes vs Class AB amps

All SET amps are class A by nature.  In a class A amplifier, the output devices are biased on for the entire waveform.  This is why they are lower power output when compared to similarly sized class A/B amps.  Some of the best amps we've heard are class A, but it's really about the overall design and build.  Plenty of fantastic A/B and other output type units out there.  

All are great if done right.

Lewinskih01/Horatio...on the Audio Aficionado site there are hundreds of pages devoted to all aspects of Dennis Had amps. That site can keep you busy for hours and make your head spin with the "what power tubes with what rectifier with what input tube" endless discussions. Fun stuff.

I have two amps. A 300b SET from AncientAudio and the 12R (solid state) from Bakoon. They sound more similar than different.

As mentioned by pretty much all posters above it depends on the designer how the amplifier is going to sound and its advantages or disadvantages. The ultimate goal is to power the speaker comfortable with more power in reserve than the speakers will need and not to impart a sound coloration onto the music.
The more important issue is a total system synergy where all the components work well with each other. Component matching to the size of your room, your taste in music and preferred listening volume.