Actually difference between class A and AB?

Class A amp sounds like holy grail of HIFI world.
But class A amp are much heavier, more expensive and rarer than class AB or class B design. Few can afford 100 LB weight of a 2-channel 100w/c amp.

Is there any actual difference between class A and class AB when listening to actual music? And what is that difference?
Interesting question. Let's add to it whether amp designers use negative feedback (NF) in Class A or A/B? As Class A seems to be the holy grail of Hi Fi, NF seems to be its nuclear waste dump.
If you don't have a Class A amp you a not with us elitist snobs, that's the difference.
The difference if fairly simple. Class A amps run at full power all the time. Class B amps run 'on demand'.

Class AB amps usually run in class A at lowest power, then switch to class B at higher power.

Whether one is better than the other is hard to say, largely it depends on the individual design.

Personally I use 30wpc Class A tubes and it, to me, is far superior to anything I've owned in an AB design. But that's just my opinion.