SET vs Class A vs tubes vs Class AB amps

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.

I think you might find the Sanders white paper on Tubes vs. Transistors to be educational.  Look for sanderssoundsystems.com or something like that. 

You want to seek a good sounding amp, and unless you have difficult speakers to drive, the type is irrelevant.

I have two systems with Class A, one with AB and one with tubes.

I couldn’t agree more that one of the most, if not the most consideration is system synergy to your tastes, and less about type/class.  An additional important factor is what type genre of music you listen to and what is the source.  For me, SET tubes deliver the best tone for voices, either analog or digital.  But it falls way short on delivering the goods through dynamic passages or rock, where a couple of different Class A classics are my choice. If digital, my best sound is delivered with tubes all the way through- SET if light voices, tube PP (monoblocks) if other. If vinyl, I lean to solid-state amps behind my 28 tube Aesthetix IO Sig phono unless it is a single guitar or similar.  I too have a multitude of options when it comes to amps- SET, SEP, PP with tubes, Class A, A/B solid state, mosfet, Bipolar, SIT, etc., etc.  and all that is somewhat irrelevant, my decisions are based on the sound.  Yesterday I did a listening session where I biamped two BEL 1001’s in stereo (one amp channel driving the base, the other the mid/treble, one dedicated to each speaker) vs the 1001’s bridged in Monoblock.  Big difference, not necessarily better, but different. The biamped implementation was warmer with a bit more meat on the bones vs the bridged implementation which had a much wider and deeper soundstage- I preferred the bridged mode.  I am starting a shootout where I am going to compare and contrast three classic Class A amps.  Stay tuned.

It's bass, not base. My little SEP Dennis Had tube amp will play anything well...from chamber jazz to Little Feat to Mahler...as any well designed amp should. If your rig is "music style specific" there's simply something wrong with the thing...don't expect much low end from tiny inefficient monitors, or relative loudness from a 2 watt amp, but otherwise don't be denied! My latest amp experiment is a Schiit Aegir...so far it's brilliant...cost less than my cables.