not yet flying, but came from the pilots expo yesterday, where i was looking at exactly this
basic rundown from how things sounded to my less than trained ears
David Clark : there were a couple of modals on display, and the X11 was among them. in terms of passive , meh, i think they have gone backwards slightly, i liked the 13.4 better. In terms of active, well, this would what you buy them for. it was ok, it didn't shine out like some of the others, but it was ok. the question becomes though, why would you pay that much for a medicore headset.
( I will acknolage at this point that, as one vender noted, everyone is diffrent, everyone ears pick things up slightly diffrently, people stress slightly diffrent qualities in their headsets )
Bose, ooh the Bose X, now that felt like a headset, again ok passive, but the active realy shone. the very first thing that i did notice, is the diffrence in the activations. the DC's jsut cut in and it sounded like you had just put your head in water, ( or had walked into a null noise room, which is I guess the point) .
The Bose set though faded in the ANR, and as there was a helo and a few fixed wing planes bussing around, I was after about 10 seconds able to sense a greater reduction in the perceved noise from them.
Avcomm : well, what i can i say, after the previous two, I wasn't impressed.
almost ok passive, but i am not sure how much that was fit, I had a hard time trying to adjust it to seal properly.
The ANR set they were showing, the AC-950, ... well, it strikes me as almost a budget set. the active was not as good ( imo) as the X11.
From the impressions formed though, the stand out model was from Lightspeed
the Lightspeed 20XLc. This I felt compared favorably to the Bose X set. in terms of active, they felt about the same, the passive on the lightspeed was slightly better, and I found the fit more comfortable, despite the slightly greater heft in the hand. I found the way that the XLc sealed around the ear entirely, and infact stood proud of the cartage of the ear ( as opposed to pinning it back against the skull) significatly more comfortable. Add the fact that my wallet is also significatly more comfortable with it ( approx $800 vrs $1500 for the bose set) .
as with most things, your milage may vary, but I for one am very glad i went to that expo.