With a box, your gonna need to put more bracing, as the preasure is not equal, with a tube, its same preasure on all sides (with exception of top and bottom) and will not need to be braced. bracing is a pain in the arse (hence the easier part), and sonotubes just look cooler. but also harder to hide a sonotube.
With long lengths of Sonotube, you can run the risk of getting standing waves in the tube. I suppose that this would happen with a box too if it had similar dimensions (or does the bracing break up any such potential standing waves??)
Anyway, if you wanted to do the column thing, I would suggest building the sub enclosure at a normal length to avoid the standing waves, and then put on a facade to look like a column floor to ceiling.