What's the story on the different amplifier "classes"?

An amplifier's circuit design determines its class of operation.

Class A amplifiers are desirable for the high quality of their sound, but the design is not particularly suited to car applications because of inefficiency and high heat production. Car amplifiers that boast Class A design are usually a Class A/Class AB hybrids.

The Class AB design is most commonly used for car amplifiers because it combines reasonable efficiency, low distortion, and reliability.

Class D amplifiers ("D" does not stand for "digital") boast higher efficiency, produce less heat, and draw less current than traditional Class AB designs, but they tend to have more distortion. Since low-frequency distortion is almost impossible to detect, compact Class D amps rule the bass kingdom.

Class T amplifiers combine characteristics of conventional Class AB and cutting-edge Class D designs for great power, compact size, and minimal production of heat.