I've got the QC-35s. They're actually pretty good at lowering speaking voices to the below intelligible level, IMO. This was also my first pair of noise cancelling headphones ever, and holy shit what a difference they make on an airplane; I'd never really appreciated how loud it was until now.

I also find that I listen to music at lower absolute volume now as a result of the noise cancelling; I'm fairly certain I did some damage to my ears over the years, and at least I'm not continuing it at the same rate now.

They are bloody expensive, though.