I was looking at that one... how does the SVS PB12-NSD compare?
I looked into both subs recently.
The PB12-NSD is far less linear than the VTF-3; the VTF-3 is ruler-flat down to around 22hz while the PB12 begins to roll off around 50hz. That said, the PB12 is also capable of playing marginally louder at pre-determined distortion limits (the CEA-2010 standard) according to the Ilkka tests, and much louder below 20hz. That is, again, at the expense of linearity. It's also worth noting that if you run the VTF-3 in maximum output mode (which most do), you get twice as much port area as the PB12. How much difference all these things make in practice I cannot tell you.
The PB12-Plus may indeed be a better sub as ParadigmDawg suggests. I could not find third-party data on it anywhere. Certainly it's prettier than the VTF-3, and it does have room-size compensation and a variable phase knob. Whether it is worth $500 more than the Hsu I can't say.
To be honest, since you've raised your budget to $700, anything you buy from eD, SVS, Hsu, or Epik is going to be a great choice.