best WOOFER ???

TC Sounds LMS 18" Ultra is I guess the end of storey !

Is it a boom boom driver or high fidelity ?

FOSTEX FW800 31.5IN Super woofer 1 of the best about for bass below 200hz. $3200 ea for new model just released march 14 2009. I would also nominate the fostex w400a-hr $2550 ea. Can be used up to 1800hz. Massive alnico mag advanced design. Dont know of a better 15in.

That Fostex FW800N would be great for tubes - I don't recall ever seeing a driver with a higher Vas.

What is best? The performance of a driver has so much to do with the cabinet and environment. That being said we did a 2 channel design for a client that installed two 18" infinite baffle subs in his room to augment his monitors. Pretty amazing realistic low level detail at the bottom end.

Take a look at the Velodyne DD series.