I've only used the QC3s on AA once but did not care for the on ear design for a long flight. The noise reduction is definitely not as good as the over the ear nor does Bose claim it to be. If you like your QC2s I'd stay with them until you can try a pair of the 3s on AA without purchasing them.

I just upgraded from QC1s to 2s and will do a comparison of my 2s to 3s on an upcoming AA flight. The 1s were too bulky to travel with and Bose wouldn't upgrade me a year ago so I bought the Shure EC4s. Great sound but noise isolation is different from noise reduction. It took me awhile to get used to the ear buds but they are so easy to travel with.

It's personal preference: on ear, over ear, in ear, sound quality, noise reduction vs. isolation. Whatever is important to you.

Here's some other threads:
http://www.flyertalk.com/forum/showthread.php?t=603678
https://www.flyertalk.com/forum/showthread.php?t=422325