That is a very good question, Which sounds best.
Given that my room is some 21' x 33', I needed more output to get into reference level territory.
From all the posts about the RSW15's dropping off after 30 Hz, I decided that some low end power was needed to supplement the RSW. The RWS15 is very very good with music and blends perfectly with the RF7's.
With the addition of the CSU's I am now feeling bass that I have never felt before. The CSU's again blend very well with the rest of my setup. I think they feel quicker than the RSW. The punch that the RSW gives is astounding.
It boils down to the range at which both subs are designed for. I love the punch of the RSW's and the deep lows of the CSU's. The THX Into is mind blowing now because of the extended range I have, something I was missing before. TPM Pod race scene is now very violent where it should be, the pulses from the engines is breathtaking.
I will be experimenting with the port plug to see what that does.
My wife has the "Queer as FolK", and "Venga Boys" CD's and some of the synthasized low frequencies in that make the floor undulate for many seconds....CSU's at work.
AC/DC "Who Made Who" has a great bass punch that goes right through you.
To sum up. For music I think the RSW takes the cake, for Movies/HT, well the CSU's are hard to beat. We all listen to both types of material. If you can afford both, I would highly recommend them.
Ben