These are the cleanest (ie... least distortion) amps made. However, I can't say I have EVER seen one for car audio. This class of amp is also the least efficient (most of the engery ends up as heat).
The most common class of amp in audio, excellent mix of sound quality and efficiency.
Class D (Not to be confused with digital)
This class of amp has become popular of late. Very efficient, but produces the most distortion.
That is not really a concern though, the class D amps are designed to run subs in a small frequency range.
The amount of distortion subs can produce before you can hear it, is much higher than mids or tweets.
I really like the class D amps, for subs, they are very small for the amount of power they can produce. Sometimes 1/2 or even 1/3 the size of their class AB counterparts.