Class D vs Class A/B for car audio: which should I buy?

Class D amps are far more efficient, run cooler, and are smaller, which is why almost all modern mono subwoofer amps are Class D. Class A/B is still common for full-range four-channel amps powering door speakers because some listeners feel it sounds slightly warmer on highs and mids, though modern Class D full-range amps have largely closed that gap.