Wait...
Doesn't this depend a lot on what type of floor one has?
Solid foundations sound better with the sub coupled to the floor. Suspended floors sound better with the sub isolated from the floor.
My friend owns one of the best audio/video integrators in Los Angeles. He seems to believe it is a no brainer,
All I can tell you, is I lived in Alta Dena in an older house with a suspended floor, and the bass sounded boomy, and tubby, until I isolated my subs from the floor.
Now, living in the Valley, in a house with a solid foundation, the subs sound better coupled to the floor.
And even at their best at the Alta Dena house, on the suspended floor, they did not sound as good as they do on the solid, slab foundation.