I own a Sennheiser HD600 and a Bose QC25. They don't race in the same league. The HD600 has better sound quality hands down and I try to use it whenever I can.

I own a Sennheiser HD600 and a Bose QC25. They don't race in the same league. The HD600 has better sound quality hands down and I try to use it whenever I can. Where the QC25 shines is the noise canceling. I fly a lot and during a transatlantic flight, Bose is a godsend. It blocks out the engine noise very effectively. I can listen to music, podcasts, videos without cranking up the volume to max. Sometimes I use it in the office to block out office noises. Every other situation the HD600 is better.