Class A amplifiers are the best you can get. Why? Because it does something that Class B (conventionel) amps can never achieve. It will give you the chills and musical involvement, as how the musician would have wanted it. And once you have owned a Class A amp, it will never be the same again. How good Class B amps can be, it just simply fails this very important skill; drawing you into the music.
But how do they do it? Conventional Class B operation causes cross over distortion. It happens when one transistor takes the wave vorm 'over' from the other. Class A is biased differently, so a wave vorm is completely operated by one transistor (or tube). The human ears are very sensitive for this kind of distortion. Sometimes it can be discribed as a 'harsness' you notice in the music.
Apart from this major advantage in sound production, It has some disadvantages too. It has a very poor rendement. A lot of the electricity it uses, will transform into heat. So, the device runs hot too! And because that, the electrical components have a shorter life span. It needs maintenance more often, so things can be replaced before they will die. As a lot of power transformes in heat, it is also pretty modest in delivering Watts. Or you need a big machine with huge power transformers like Krell used to built.
Unfortunatly, nowadays you don't see them appearing anymore in the world of high-end audio. Simply because the new regulations (environment) doesn't allow you anymore to built things that suck up a lot of electricity and only uses a small amount of it to what is is designed for. I can remember an interview with Antony Michaelson, founder of Musical Fidelity. He would have still be making Class A ampflifiers, if the regulations would have allowed him to. He knew, that there is just no subsitute for the musical performance.
The good thing is that there are so called 'Class AB' amps. Until a certain amount of Watts it operates in A. Then when there is a demand for more power, it switches into B. So, best of both worlds combined. However, it doesn't sound as sweet, but it comes close.
Same goes for tube amplifiers. In Class B they sound great, but in Class A it is just superb. And when playing singled ended, it will blow you away. There isn't simply anything better. Describing it, is hard. Same as good wine, you need to taste it for yourself. The first amplifier ever made was a single ended machine. And it is still lonely at the top. Of course, the new Class D amps getting better each day. For example, I was impressed when I listened to the ampflifiers of Bel Canto. But untill this day I miss my Musical Fidelity Avalon.....