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

Lower power consumption with most A/B amplifier designs. They tend to be popular in devices like DACs. Due to the nature of the Class A topology, they are very inefficient with electricity and typically generate a lot of heat. My Class A systems can only be run once or twice a week...otherwise my power bill will go up! 

Class A has a conduction angle of 360 degrees, whereas A/B is less.

In theory, this should translate to a more controlled and linear amplification of the signal. In most cases, Class A amps have more of a "grip" on the signal and can be "straight wires with gain." Everyone hear probably knows what I mean (see what I did with that spelling mistake) lol 

yep. So class A is superior if it is designed well without compromises.

Orpheus10, I don't have such a hearing as you imply, but my ear is quite sensitive to some aspects of a sound. 
Let's not transform this thread into tubes/transistors debate. Sure, ultimately tubes rule.
That's what we are trying to talk about - designs without compromises or almost without compromises. Heat, space, cost, look - this is all BS, just certain side effects. Done right it should always be full Class A design. And since Class A requires high level power supply, that's an additional advantage, that's where it all starts - with a power supply.

Audio Research amps run A/B and top of the line ARC are the best I've heard. I'm sure there are better, but they are the best I've heard.

I think balanced and unbalanced is also significant because balanced interconnects are not affected by long runs.

Anyone in the NYC area - Northern NJ area who would like to hear the differences, send me a PM.  I would be more than happy to show you differences in equipment - Class A tube, Class A SS, Hybrid amplifiers, Direct Heated Triode components, etc.  I'll even supply the pizza.  Bring your amp if you like!

Happy Listening.  

@audioman58That being said , inside the Quality of the parts have much more to do with the final result of the sound.

I would have normally agreed with your statement but last night hearing an OK to good parts preamp it was so close in sound to the better parts model we build I began to wonder if paying for custom transformers, resistors, capacitors, separate chassis, etc. was worth it.  So close it was confusing to us and made me think that we have now come full circle.  Still point-to-point wired and good parts but so close.

Happy Listening.