You might want to read through the Wikipedia page on the classes of amplifiers:
https://en.m.wikipedia.org/wiki/Power_amplifier_classes?wprov=sfti1
Class A, AB, and B were once very popular in car audio. They are analog amplifiers, and generally had very good fidelity, meaning that the sound was amplified with little distortion until near the maximum power.
A Class D amplifier works differently than an A/B amplifier in how it processes the signal and outputs it. Instead of a smooth spectrum of outputs, it has a series of finite outputs.
In the early days of class D amplifiers, they didn’t have quite as much fidelity as the analog ones. As such, they were generally reserved for low frequencies and high power, much like you would need for a subwoofer.
However, as technology improved, they became virtually indistinguishable in fidelity to the analog amplifiers, and became to be used in many different applications, including speaker amplification. One major change was that they were improved to switch faster, allowing it to reproduce higher frequencies more accurately.
For automotive use, I solely go with class D amplifiers. They are far more energy efficient than analog units. This means you don’t need as big of an alternator to run the same power, or you can use more power on the same alternator. It also means the amplifiers run significantly cooler, so ventilation and overheating is much less of a concern.
For example, in my F150, I have 3 digital amps: A 4 channel amp that puts out 150 watts RMS per channel, and 2 subwoofer amps that put out about 1200 watts RMS each. All 3 are Class D amplifiers. At around 80% efficiency, they combined can consume up to around 300 amps of current (normally less, even at full power), which a single 370 amp alternator can easily provide. However, if I had gone with analog amplifiers, I would need around 450 amps from the alternator, at which point I would either need a 2nd HO alternator or additional batteries to fill in the gap. In addition I would need to very carefully mount the amps, as they would generate a LOT of heat.
So for automotive use, stick with Class D. If you really wanted a high fidelity sound system in a completely deadened room then consider analog.
That said, analog amplifiers are often cheaper, and will work fine in many smaller systems.
