I started with a DC H10-13.4. I eventually added a Headsets Inc ANR kit to it, which dramatically improved the noise reduction. Unfortunately, it didn't do anything for the comfort. You don't realize how uncomfortable a headset is until you try one that IS comfortable.
I had to start wearing glasses a few years back, and the temples of the glasses really started to bother me even on short flights with the headset pushing against them. I eventually bit the bullet and upgraded to a Bose A20. I did quite a bit of research, but was limited to TSO'd headsets due to company policy. I went to a local avionics shop and tried a few different ones, including the DC ONE X, but liked the Bose better. (They didn't have the DC Pro-X).
I've been using the A20s for about 8 months in the Q400. While it is far more comfortable than the old DC H10-13.4, I still seem to be adjusting it constantly, and I still have the issues with glasses, though not as bad. They're fairly comfortable, but I still find myself wanting something more comfortable, and for the price of the Bose, that is unacceptable in my opinion.
Based on what I've read, and what I've heard on here, I just bought a DC Pro X. I plan on bringing the Bose and the DC Pro X with me on a 4 day trip tomorrow, and I'll try them both side by side in the Q400 for the duration of the trip. I'm either going to return the Pro X, or sell the A20s after the trip. My deciding criteria will be comfort, as I believe that both of them will provide quality sound and sufficient noise reduction.
My initial impression of the DC Pro X is very positive. They seem a bit more comfortable with my glasses as they aren't constantly pressing against the temples. They're a good bit lighter too, which doesn't seem like much, but after a long day of flying, I don't dare underestimate the impact of that little bit of weight reduction. They also seem to have a little less clamping force than the Bose as well, which I like very much. And
@SurferLucas is correct... the Bluetooth is kickity assity, and music seems to sound just as good as the Bose.
I'll post back and let you guys know which one I end up keeping.