smoknhothonda, there are a lot of brands out there. make sure you get something that will do the job right for you, plus THD in a sub amp wont matter much as you will have that in the boot and wont be able to hear it distort anyway, not 0.00000001% anyway as funkdr claims

theres a limit to how far you can go before specs become non-evident while the car is going and that what the car is meant for in reality, not to stand still to listen to an audio system, thats why we have whats called home HIFI