I've owned 2 of what most consider to be the top 3 noise cancelling headphones on the market; the Bose QC35 and Sennheiser Momentum Wireless 2.0
I still own the Sennheisers. Here's why:
The QCs sounded completely different in noise cancelling mode to when it was off. This was the first problem. I didn't always want it on, due to the pressure on my ears and the horrendous thumping sound when walking (somehow every review seems to miss this). Common across all of Bose' lineup. They had a very aggressive 'V' shaped sound signature with NC on, resulting in a very unnatural sound. They'd also struggle at higher volumes, when you're listening to an awesome DnB track, eagerly awaiting the kick to, well, kick in. You'd be left with a very sloppy and boomy thud. Though, comfort is second to none.
The Sennheisers aren't perfect, but they're close. Comfort is almost as good as the Bose (even for my large ears). Sound is natural. A definite emphasis on bass, but somehow it's only really noticeable when you're music is begging for the extra 'oomph' (Rudimental - Too Cool is a great example of where these shine). Battery life is strong. The noise cancelling is what I'd deem 'sufficient'. It's not so extreme that there's a horrible pressure build up like on the Bose, but good enough that I've never felt I wish it removed more noise.
More importantly, the wireless on the M2BT is, from what I can tell, entirely fixed. I can be in an entirely separate room (albeit separated by plaster) and have no wireless troubles at all.