After all these replies I've seen to your answer, none of them truly helps you with your decision. I've searched forever to find the perfect cans and IEM's. I've owned a lot. It does NOT matter what others tell you. *you* need to listen to them for yourself. The ONLY place I've ever found that you can test ALL the high end NC cans (and even great IEM's) is Inmotion Entertainment found at nearly all the airport hubs. They will take their time and let you listen to ANY headphones they have for as long as you need to make a good decision. Most terminals are noisy enough to test the noise cancelling yourself and also take time to tweak the sound with any audio player you have. I personally loved how comfortable the QC15's were, but I ended up purchasing the UF8000's because the NC was 'good enough' for me and sounded much MUCH better. I use an iPhone 5 with the denon audio player because of its infinite point parametric EQ (and even works with ALL TuneIn Stations) and a FiiO E6 external headphone amp (which you can find for $25 bucks shipped online) and does wonders with the UF 8000's. I am seriously impressed with the frequency response. My only complaint is how uncomfortable the UF8000's are. I am a road warrior and fly 1-2 RT flights per WEEK so I'm in a plane a lot.
The other comment I need to make is for IEM's I'm very impressed with how good they sound if you pick the right ones. The ONLY way I can get them to block ANY sound out is to use the Comply foam PROFESSIONAL line of inserts - and ONLY those tips! Again, Inmotion also will let you demo these as well and they do an AMAZING job of blocking sound compared to any other foam/silicone inserts. Any other comply foam insert doesn't block sound nearly as well.
I really hope I helped. I'm very unbiased in my answer and want you to make a good decision by giving this store a shot the next time you're flying through an airport, even if you have a pair of headphones. It will help you compare what you have to the other options out there.