Depends on what model your looking at. I've always been a fan of the Treo SSi if you want a low powered sql sub. But the RE XXX is known as one of the best as well.
Tell us what models your looking at and we can point you in the right direction.
the ssx is in the same category as a dd9500 except it gets much much lower and absolutely is a ground pounder. Then again the dd plays higher and gets louder on a TL so its all what you want
The main difference that I know of(and I like both companies products) is that the customer service at Treo Engineering is terrible. Other than that they make solid product.
im just not sure what to get i mean i want it to be loud the seats fold down. but what about an alpine r 15? or just 2 12 r's? just want something that isn't distorted highs in the sub and a sub that will hit lows pretty nicely .i had 2 12's in a ported box 34hertz the subs were dual 4 ohm and were audiopipes lol. with a maxxonics amp 800 rms. and it hurt my ears in my sunfire. so anything thats gonna sound better than that and be louder is a plus.