I'll break down the differences in plain and simple terms:
Class D = cheap power for high school heroes and wannabees who fail at life and therefore must exert their bad poetry to a beat on those around them. It is as if they are saying "Hey, look at me, I am somebody because I run 3,000 watts RMS to my subs but power my factory speakers off the head unit!" Don't get me wrong, they also make great power for burps in competitions, so they do have their place.
Only the real men run Class AB! Why? Because we don't care about DB numbers, we like how our music sounds. We also don't care about the lengths of e-penises by riding the current boner product of the month because our amps have lasted years, and in some cases decades!