Ultimate sub?

This one from Rhythmik has about as much low end extension as you could ever require. It's down 3db at 14hz. It's a sealed box with a 600wpc dedicated amp. I use a pair of their 300wpc 12" subs in a pretty large space and have apparently limitless clean SPL available. (I say "apparently", because tho they stay clean - to my ear - and go louder than I'd ever care to approach, I've never measured for THD).

Although I've never heard this model, I suspect that you'd need a giant room and some very unusual program material to find the limits on a pair of these guys.

http://www.rythmikaudio.com/F15HP_specs.html

BTW,

Rythmik also makes a vented (ported) version of the model. Here are some test results, if you're interested. Outside of group delay below 20hz, these are pretty impressive numbers. The subs go deep and loud and stay clean (for such low frequencies, anyway).

http://www.avsforum.com/t/1342986/rythmik-audio-fv15-hp-data-bass-test-results

If your willing to spend 12k or a tad less , the Ken Kreisel DXD12012 in a Quattro stack ( 4 subs 8 drivers in a push pull configuration with 10hz extenstion) in a pulsar configuration would be mind boggling and extremely musical, I have one DXD12012 and it will change your definition of what "true bass" sounds like! clean , clean, clean!

I hear you Jmc, I get the same thing for saying ,"there's no best....".

Check out SVS,they make real nice subs.