I went with HSU VTF3 MK3 becuase it was the absolute best bang for the buck. For 650 bucks this sub is absolute killer. My room is about 15x22x8 and this sub is more than I'll ever need and hits down to 10-12hz @ 100db at 1/3rd of the gain and -3 on my reciever.
Unbelieveable deep bass. Its not even the sound its the feeling. Also HSu customer service warranty is top notch.
On the flipside SVS is also known to be just as good with the customer service and build quality. However they are a bit pricier and do not offer as much bang for the buck. Not to say that SVS doesn't make fantastic subs jut that the HSU VTF3 MK3 @ $650 easily competes with $1200+ SVS and otehr brand subs.
I love my Mark III. I am not a fan of Klipsch subs although I love the speakers. I run 2 x RF-82s, 1 x RC-62, 2 x RS-52s, and 2 x RB-61s and the Mark 3 and the sound is incredible.