I tested the Denon AH-NC732, the Audio-Technica ATHANC7 Audio Technica ATH-ANC7B Active Noise-Cancelling Closed-Back Headphones, the JVC HANC250 High-Grade Noise Cancelling Headphones and the Bose QC15Bose QuietComfort 15 Acoustic Noise Cancelling Headphones.
Let me start by the worst of them as it was clearly the JVC, despite the reviews I checked. Actually, given the reviews, it was the first one I bought. However, soon I placed them, the sound was not good at all. The noise cancellation was ok, but you could hear a slight buzz. I return it
Then I bought the Audio-Technica. The sound is wonderful as well the noise cancellation, the best of the first three. I return it because the noise cancellation only works for the person using the headphones :-). Someone on the side can hear very well the music being played. Despite what some reviews say, it has nothing to do with the sound volume you are using. The headphones just leak very easily.
There was another reason that made me return them. They are just too big! As I want to use the headphones for air travelling, I suspect that with these headphones, someone would ask me if I was not mistaken as I should be on the groung maneuvering the ground movements of the plane :-) I return it.
Then I bought the Denon's. They were the best considering the sound quality and the noise cancellation performance. You hear a slight wiss with the NC on, but it does not bother. Also, they are very comfortable (I used them from Frankfurt to Houston 9h flight). I kept them...
Last, the Bose QC15 are really good. I test them in a Apple store during the Christmas shopping period. I was amazed with the NC performance. Actually, it was so good that I felt a bit dizzy in the end. I think this is something that one will get used to. The sound was just the best and much better than the Bose QC3 in all spectrum.
However, they cost more than twice the Denon's and not sure at all if it is worth it. I had trouble to justify it for me, although I travel a lot and I can afford them.
Also, they are bigger and heavier, which is important to consider to fit in a bag with computer.
At the end, considering all the money lost with the returns, I may have been better off if I went directly to the Bose.