Why would anyone want class AB amp when class A always sounds better ?

You could try and offer a better one, wolf. Why are you yelling here ?

Implementation is always important, but that's not all.

Class A does NOT sound better (as the thread starter claimed). I owned pure class A Krell monoblocks which definitely didn’t sound better than my current Pass Labs class A/B mono blocks. This statement of the threadstarter is way too general ...just like a V8 is always faster than a V12 or boxer 6 .... 

I had a lot (or heard -) of class AB amps (high-end): Luxman, Esoteric, Hegel, Audio Analoque, Jeff Rowland, Accuphase, Mark Levinson, d’Agostino,...not of them all ,sounds better than Ear Yoshino 509 monoblocks or Wavac MD 805m. : the purity, detail, 3D. If you really enjoy your music, this is the best. You can’t put it very loud,  but you have to to really enjoy it. Tubes get warm and have to be replaced after a while,but a real music lover will take that in. In transistor, I had a few class A amps:some of them sounds to “dark”, detailfull,rather “flat”.

Class A does NOT sound better (as the thread starter claimed).

He doesn’t mean different manufacturer amps.
The same amp/s will sound better without any xover distortion, and the way to get it is with more Class-A bias if all else can take the extra juice that it needs to do take that extra class-A bias, and it will sound better for it.

Just have a listen to the Halo JC1 monoblocks they have a switch on the back that raises the Class-A bias quite considerably, you clearly hear which sound better, same with the Gryphon Antillion with it's switchable bias.  
Cheers George