It's all in the seat of your pants.
I think it's purely a personal issue. I like the increased road feel the HDs give over the Cs. I felt that the suspension was "squishy" prior to going to HDs all around. There is some rattling and if there's a loose CD jewel case on the passenger seat or in the door pocket it will create a racket, but the car feels lighter and quicker. Not everyone would agree. Some who have driven my car are put off by the stiffness, commenting on how it seems inappropriate for a Benz.
On long trips, the car just seems to get more and more responsive. That's probably hyperbole borne out of a love for the machine, though.
2003 Dodge Durango SLT
2002 BMW E39 530i Sport
1988 Mercedes 300TE
2003 Chevrolet Suburban