I used the Vandy subs in my system for a number of years and they were certainly excellent for augmenting the bass. The one problem I had with this sub was that it placed a crossover directly in the signal path. Even though I used Vandy's highest quality crossover (not the little black box that comes with the sub), I could always hear some upper midrange grunge when this crossover was placed in the system. It got to the point that, when I wanted to listen to music that did not contain deep bass, I would disconnect the sub. Of course, at the time I was using Quads as my main speakers and these are quite revealing of midrange anomolies.
I am now using a REL Strata III. It does not produce as much bass as the Vandy but it is close and it has the advantage of not introducing a crossover into the signal path. I suspect you already knew that this was a significant advantage of the REL design. All this to say, if you are using the sub in a music only system and if you are sensitive to anomolies introduced in the midrange, I would be careful with the Vandy sub system. After experiencing the REL, I could not live with the Vandy again. I cannot comment on any of the other subs mentioned.
I am now using a REL Strata III. It does not produce as much bass as the Vandy but it is close and it has the advantage of not introducing a crossover into the signal path. I suspect you already knew that this was a significant advantage of the REL design. All this to say, if you are using the sub in a music only system and if you are sensitive to anomolies introduced in the midrange, I would be careful with the Vandy sub system. After experiencing the REL, I could not live with the Vandy again. I cannot comment on any of the other subs mentioned.