Why do I like Class AB better than Class A?

I don't think Plinius designed the SA10x and SA Reference/250 to be Class AB amps but they wanted the amps to be left on all the time, so providing that AB switch provided owners a way to leave it on 24/7 without busting the electricity bill.

FWIW, when comparing Threshold model amps that had similar chassis, though with differing bias, etc., that were sold as different models with either Class A or Class A/AB (Class AB) output; other than running hotter and with lower total power output, the Class A amps were smoother and more laid back, while the Class A/AB (Class AB) amps ran cooler, had more total power output, were more dynamic and more upfront, though not as suave.
Depending on the speakers, the room, preferred live musical event seating, sonic priorities, and of course budget, I could imagine different people having different preferences.
FWIW, I'd prefer the best of both worlds, cool running, dynamic, neither laid back nor forward, suave sounding, Class W hatever. So far it's typically been high powered Class A amps that have come closet to most of those ideals (except of course for the heat, which I could most easily make an exception for), unfortunately the costs of such amps have just as typically escaped me. High biased Class AB amps have so far become the prudent choice, at least for me. YMMV.
Class D might change all that, we shall see.

it is possible you prefer greater resolution in the ab mode that you feel is lacking in the a mode.

i would imagine that in class a, your amp is an electric bill.

the plinius was recommended to me to use with panel speakers.

i would like to hear what they do with electrostatic speakers, but have not heard them.

Mrtennis, you can expect most transistor amps to be somewhat bright and lacking bass on most full-range ESLs like the Quad ESL 63.

The impedance curve of such speakers and the way they operate simply does not favor most transistor designs. there is more information at this link:
http://www.atma-sphere.com/Resources/Paradigms_in_Amplifier_Design.php

I also almost always prefer AB to pure class A. I do love my my Reimyo PAT 777 but it was purchased specifically to drive the ribbon teeters in my self designed 3 way active speakers. Push pull simply sounds more focused, and real in most cases to my ears. Now I do remember loving a pair of Aleph 1.2' I had in my possession briefly about 17 years ago with a set of Miller modified Infinity RS1-b panels I used to own and that combination was STUNNING (on certain types of music). No saxophone and the Emit drivers were subject to resonances that destroyed the sound :(