The AKG N60 NC reminds me a little of Beyerdynamic's T51i on-ear headphones. It isn't quite as revealing as the T51i, but it offers clean, well-balanced sound with smooth treble, warm midrange and a tighter bass than the Bose QC25 or QC20, which come across as slightly more laid back (even if Bose did improve the treble response in the QC25 and make it a more exciting headphone).
Whenever you introduce active noise canceling to a headphone, you lose a little bit of sound quality, but the N60 NC succeeds because it comes across sounding more like a passive headphone -- and by that I mean natural and not overly processed.
Because the QC25 is an around-ear headphone, you get a bit better noise isolation from its design. But for an on-ear headphone, the N60 NC's memory-foam-equipped earpads do a decent job sealing out noise even though they rest on your ears, not fully enveloping them.
Typically, an around-ear headphone offers more open spacious sound, but I thought the AKG had a little more depth and richness to it than the QC25 -- the AKG sounds like a bigger headphone than it is.
But the Bose has a small comfort advantage, particularly over longer listening sessions.
As far as other competing models, I also liked the Philips Fidelio NC1, another on-ear noise-canceling headphone. But that model costs more and doesn't perform quite as well overall -- both in terms of noise cancelling and sound. The AKG is a notch up.
A worthy Bose rival
Minor gripes aside, this a well-designed active headphone that's worth considering over the Bose if sound quality is your highest priority in an active noise-canceling headphone.