If you're concerned about losing money by buying a sub which you cannot demo and then not liking it then get a used REL. Almost cetainly you'll like it, and in the unlikely event you don't you can resell for the same price. I've also heard many people rave about ACI Titan 2 ... and ACI apparently has a good home demo policy. I have never heard the Vandersteen, but they seem to sell well used, so you could probably do the same as with the REL ... buy and try ... sell if you don't like it.
subwoofer suggestions
I am looking at adding a sub to my 2 channel music system. I am using a B&W Nautilus 804 speaker with MF m3 integrated amp and Linn ikemi cd player. People have told me the Linn sizmik, b&w asw 2500 or mirage subs are good. I don't want something too big but I want nice tight bass, not boomy. I here REL is good but there are no dealers in Toronto.