http://forum.ecoustics.com/bbs/messages/1/1041.html
Three Subwoofers Face Off: SVS 25-31PCi, HSU Research VTF-3, and Axiom Audio EP-350 Subwoofers
"Final Thoughts
If you haven't figured out already, the SVS emerges as the winner of this face-off. You'll also be surprised to learn it is the least expensive of the group! It just goes to show you that more expensive doesn't always mean better. At just $549, the SVS is the best bargain in bass. "
SVS seems first, HSU second, and Axiom just doesn't make good subs, as it seems. I've seen a lot of other reviews with the same train of thought(SVS first, HSU at a close second with the upper models, and Axiom last).
Hope this makes your decision easier.