There's something I get from an under-quilt that I've never had from a CCF pad---a sense of WARM coming back at me. The trapped air in a quilt warms up and radiates the heat back. The pad gives me NOT COLD. Which is a good thing, to be sure. But in my experience, different.
That's the best I've heard it described yet and I agree completely. I also like the fact that I don't wake-up with my backside wet from sleeping on a pad; that's always a nice sensation climbing out of the hammock on a cool day.