SVS or Velodyne

I have a Rythmic 15" in a custom cabinet built by Salk Sound. Great, super tight base that really digs deep. Of course the cabinet is probably a 30" cube made from 1" MDF with enough bracing inside so you can set a turntable on top it and never skip. Weighs about 220 lbs too. Nobody ever accused Jim of cutting any corners building speaker cabinets. 

Those Salk built Rythmiks are great. You can also buy the DIY F15 kit and build an enclosure yourself, bracing the hell out of it as does Jim. The Salk wood finishes are really beautiful.

I thoroughly enjoyed my SVS’ for home theatre effects.I stopped using them with music I wasn’t happy with there performance. Rythmik gets a big yes from me. 

Try and listen to the Hsu  VTF-15H MK2 if you can.
Amazingly good and a lot of flexibility.

I have a SVS sound cylinder in my home theater setup. I like it for music and movies, but never tried it in my 2 channel system. 

Rythmik seems to be very well thought of around here, fwiw.