Best Big Sub? or duals?

I'd opt for two Fathoms. I use two now and am very happy with the sound. However it depends on how much work you want to do. If you want to set it and forget it for home theater, then if you can swing it the one Gotham will sound great, I believe. Two subs (or really one sub if you want the best sound)take some tweaking especially if you are using them for two channel only as I am. I was very impressed with the setup directions and performance of the auto setup procedure from JL Audio. The setup system from Velodyne is much nicer but one cannot run balanced cables only single ended. The Fathoms work well with my Salons and a friends electrostats so I'm sure they will work with the Vandersteens as well.

Look at the SVS PB13 U before considering anything
the Epik conquest as well. both have CONSIDERABLE output
I own an SVS PB13 and I would personally go with the ED A7-900, The Conquest or the Ultra if anything, Have no personal experience with them, danley as well.

I have an SVS PB 13Ultra in my 23x18 basement with carpet on concrete and it shakes(O.M.G) with great finesse, detail, dynamics, very low distortion & extension is unbelievable. Usefull tuning ports too......ALSO: I'm buying a Sistrum SP-101 stand for it to raise it up off floor as suggested by many. Can't wait ......buy 1, or maybe 2 and shake a city block.....It'll rip yrrrr chest apart too.....
REGARDS Bacardi

As a Velodyne dealer, I'm going to recommend dual DD18's for that size of room as I have the most experience using these subs in that size of room. To be honest, I don't think a single sub of any caliber will get you what you want.

Other options are dual JL Fathoms or Triad Platinum Powersubs. On a budget, the HSU subs are tough to beat.