I have the QC2s and am very happy with them.

I like the AAA battery as I simply carry a spare in case it dies while traveling. If I forget my spare I can easily find a AAA at an airport shop, probably would not have the same luck with the other one.

I also think the physical noise blocking of the earcups help to further lower the sound levels from just simply the noise cancellation.

Finally years ago I worked at the apple store and the QC2's just seemed to hold up to the daily use and smashing by customers than the QC3's did.

On the flip side if you like to sleep on the plane a lot the QC3's will probably make that more comfortable than the 2's.

That said I think either is a good choice...I just prefer the QC2's.