It's unfortunately VERY difficult to do a proper side-by-side comparison of headsets. Essentially, you'd need to go flying with a sample selection.
I have bought the Bose-X and did just that with my old (non-ANR) set and the difference was simply amazing. I've also got a request from a friend with Sennheisers to do just that. As we live (and fly) in different countries, this may have to wait a little while, though. I'll report back.
I'd say the Boses are great, however only with the ANR on, the passive attenuation is crap. Others have commented on the Clarity Aloft ones (which I considered, but couldn't find a reseller in Europe with a money-back guarantee as with the Bose-X). They sound very interesting, however as I always wear earplugs when a pax on a longhaul commercial flight, I'm not so convinced of having something stick in my ear for long periods of time (as a pax I'm asleep, but still don't like the feeling much).
HTH