Amplifier classes

[eg]

Going thru brochures I see that some amplifiers are classA, some class AB etc.
What are the different amplifier classes out there?
Any reason if one class is preferred over the other?
Does this apply to both poweramp and the preamp portion?

[Racerx2k]

The classes refer to the power section.

Here's a link that can help explain it to you better than I ever could:

http://www.duncanamps.com/technical/ampclasses.html

[eg]

Thanks for the link.

How about the preamp section, are they designed to be operating in a certain amplifier class?

[eg]

After some reading I found out that class A amps are less efficient then class AB/B amps but do not suffer from crossover distortion, which I think would influence sound quality.

Does that mean technically Class A amps sound better?