I'm very happy with the 8104D. Powers a pair of 10 inch medium duty Kenwood subs very well. My subs aren't capable of bass that would blow out windows, and I didn't expect the amp would change that. The amp make the subs hit with good volume and quality though. For the money, I don't think you could do any better. This model doesn't have an internal cooling fan, but I've never had any sound cut out, and it's never felt more than warm to the touch.
It is my first Kenwood amp, but I've installed several amps over the years.
My ratings below take into account the price.