I will disagree with Latitude over the Carbon Fibre bikes. My C.F. bike took a lot of sorting to give as compliant a ride as any of my other bikes. I was under the impression that C.F. has flex built into it but not all of them do. The main components for a comfortable ride are the wheels- the tyres and tyre pressures. My most compliant ride is the aluminium framed lightweight Boreas Ignis. This is a race spec frame and boy is it comfortable.

But saying that- My ride of choice now for my area is the C.F.Giant- but that is due to its climbing ability and the fit of it.