I had considered the Energy but listened to that and the Supercube at BB, the Supercube seemed better, not sure how biased that setup was though. Some of the posts I read seemed to think the minivee was superior to the Supercube so I hadn't looked much more at the Energy (or Supercube).
Was my logic flawed?
First, the SVS is definitely the way to go if you don't require the mini size of the others!
In what aspect(s) did the supercube seem better?
It is pretty hard to compare subs and BB doesn't usually do much to help the setup (not to mention guys like me screwing around with the knobs on the back.
Matching the levels, setting the crossover correctly, location of the sub and listening location, and making sure both subs are equivalently setup if Audyssey (or equivalent) is employed - any one of these alone could make a huge difference in a sub's apparent performance.
That is also a great advantage of going with a sub like the SVS which has a reasonable amount of measurement info (from the SVS site - but they have historically been comparable with third party measurements).
The link on the Energy/Mirage included some measurements by Steve Holden, which seem pretty good for a 9" cube, beating the mini-vee on some counts.