Which sub is better for audio

Assuming you mean a sub primarily for MUSIC (vs. home theatre), then I also highly recommend the Rel Strata III (which is a bass extender--you mains still get full range signal, and you set the sub to come in just under the mains' low range) or the Vandersteen 2Wq (traditional 80hz cut-off).

I have the REL Storm III which is $1800 for black and $2000 for wood veneers. They sell for $1500 demo/used mint on occassion here. The Storm III and Stratus III will perform basically the same; the Storm will go lower. The Vandersteen 2W is also musical. I have not heard it myself, but for under $1K the Monitor Audio ASW-210 has gotten some good reviews for being musical.

I am using a Bag End with Von Schweikert VR4 Gen II's. Seamless Extension.Magic Audio in Atlanta is the place to get one under 1k dropped shipped direct from Bag End.

For used only, the B&W Matrix ASW-800 is also very nice.

Used several of the above subs. The best one on a dollar per unidistorted dB of output is the HSU1220HO. A real deal in audio and don't let anyone who has not auditioned one at home tell you other wise. Check Issue 15 of the Audio Critic assessment and measurements for the straight goods. The others are not as good as you may think (or their designers for that matter) Been there, done that, wasted a lot of money...