I have the Sony MDR-NC20's, as well as the Bose Quiet Comfort 2
I just bought the Bose at Denver Inter Airport
First off, for the money, the Sony MDRNC20 is an AWESOME deal!! Excellent sound quality, great noise cancelling on airplanes and other noisy places, and VERY VERY comfortable fit
http://www.crutchfield.com/cgi-bin/S-OG8IgLjRyiH/ProdView.asp?I=158MDRNC20&s=0&wm=su
The Bose is VERY expensive, but here are its pros:
1. It really does have great sound quality (although, the Sony is very similar)
2. Its noise cancelling is AMAZING --- if you are on airplanes a lot, then this is the headphone to go with
However, the Bose has dissapointed me, in that, I don't think its very comfortable....... I sometimes find myself getting small headaches after wearing it for more than an hour, mainly because the phones press against my ears very tightly (I could also have a big head?)
For that reason, I may return the Bose and revert back to Sony
So my overall analysis ---
The Sony is a great, great purchase!
The Bose is also very good (provided that it doesn't give you headaches)....... however, try the Bose out before buying them --- they are available to try out at all Apple Stores and most airport terminals
--- and take it from me, they will perform awesomely in airplanes!