I've recently bought a H6, after a long hesitation between the B&W, the Momentum the Sony Z1000 and so, the H6.
Let's be honest, they are all very good headphones, and I'm pretty sure you can buy any with confidence.
And let's be realistic, you can find similar quality headphones for much cheaper.
Bang & Olufsen was also, to me, some kind of an European Bose...well made products at unreasonable prices (Vs audio quality).
But the listening session has convinced me they were not that bad.
I first tried the Sony, but even if the audio part is rather good, it wasn't as confortable as the others, and I could not see any thing to justify the price range.
Then the Momentum, which looks terrific in brown.
But my first impression for that one was : IMG, it sounds like my HD25 !
The second impression revealed the Momentum is less V curved than the HD25, and much more confortable.
I don't know if the driver is different or not, but the sound signature is very similar to me, too similar to buy the Momentum.
The P7 was originaly my first choice.
I've had many B&W speakers in the past few years, and I really liked the look and the built quality of the P7. The leather is nicer than on the H6 and it is confortable.
But after a quick listening session, I thought it was not necessarly what I was looking for.
At first I tought it was neutral as it has not so much bass, nor treble, but after a few seconds of Melody Gardot...that P7 is flattering voices.
It is not a CONS, some might like it, and I'm sure I would have been able to live with that, but again, that warm sound was not was I was looking for.
And it sounds even warmer when you're comparing it with the Bang and Olufsen H6.
That one has been a real surprise to me.
First of all, because I trust B&W Sennheiser or Sony more than B&O.
Then, because it sounds very neutral.
It can play anything right, from Electro to Classical, without adding or removing anything.
Not as warm as the P7, not as boomy (in the good way) as the Momentum, just good with any kind of music.
Finally, even if the leather pads or the head band are not as nice as the P7's, it is well made (thanks the chinese), it is very confortable, it is nice, and you don't really pay attention to it (which might be good if you are using your $400 headphones in the train or the bus, as I do).
Excuse my english, my french is way better. :)