there are many different amplifier architecture types and that discussion is a very deep rabbit hole. In car amps, youre mainly going to see a/b and d. Class d amps are far more efficient meaning they will put out more watts per amperes consumed. Class a/b is what the industry relied upon for decades and is the old reliable. Youll hear tons of folks argue about a/b sounding better than d and im in that camp, but its hard denying the sheer brute force of class d amps. Formerly relegated to the 200 hz and below due to the technology of the day when they hit the scene in the late 90s. Then theres tubs amps like butler. Not at all ideal for a car with subs, or a car at all really due to the vibration. Get a good powerful a/b for your fronts, big ass class d for your subs and a stout electrical system to support them all. Also, be careful of the brands you buy and even the models within known good brands as some of the brands that are known to be good make a line of duds. There are also tons of brands that youve likely never heard of, even if youre familiar with the car audio game. Trust me, the brands of old are all but dead and gone, or purchased by **** companies looking to cash in on a name