The Outlaw EX model is for all practical purposes the same as the HSU VTFMK3-4 and will have the most output and dig the deepest and if going with just one sub would be the clear choice.
But a pair of the Outlaw Plus models would trump a single EX and at $499 each are a heck of deal. This and the Rythmik would be close in output and extension from what I gather.
The Rythmik has a servo controlled driver and again just based on user comments would most likely sound better. More detail and subtlety with less distortion.
The SVS PB1000 digs about as deep as the Plus and Rythmik but gives up some output over 30hz compared to the rest. It's still a good deal, has a great warranty and a risk free 45 day in home trial. A pair are $949 delivered.
Klipsch RF-62II, RC-500, RS-400, SVS PC12+,
Def Tech SC8000
Harman Kardon AVR 1600
PS3, Apple TV, Sharp 70" Qattron