Let's consider the potential noise from the drain when the toilet is flushed. It is widely believed that cast iron, of all the commonly-used materials, is least likely to be noisy when volumes of water are flowing through. I suspect that every installation will differ on the noise, if any, because every installation is different.
My PVC is really quiet but I have seen some PVC that is noisy.
One assumes that the newer toilets will cause less noise in the DWV due to the decreased water volume compared to the toilets of 30 years ago.

Our plastic pipes in the previous house made it really obvious what people upstairs were up to. I think though that it was the horizontal runs that were noisier than the vertical ones. I've also had a lot more problems with plastic toilet flanges warping, breaking, and leaking than with the cast iron ones.