Are you doing separate trips, an open jaw, a stopover, or what? If you're returning from LHR, I'd do LHR-CDG-IAD just to simplify the CDG transit as much as possible. IAD-CDG-AMS is going to require clearing immigration in CDG and probably a dozen terminal changes with confusing signage.

That said, I just flew CDG-IAD-ATL instead of taking one of the CDG-ATL non-stops so I could ride the A380 (Y seat on the UD) and thought it was great. Much quieter than other planes. I returned straight to LHR on a DL 764 and it was noticeably noisier.