Now that is an interesting question.
I have had a set of Bose headsets for quite a number of years. They are a terrific product.
When David Clark released the X11 headset, I bought a pair, due to the ability to integrate a mobile phone/UHF radio/music player with them. In my opinion, the Bose had better ANR quality, but the X11 was more comfortable to wear, and the phone interface was a "must have" feature. Overall I quite like the X11 headset, although many on here will beg to differ (Including a well known Dr). I have been using the X11's for the past 18 months.. and Mrs Beach has had to use the Bose.
I had the opportunity to try a set of Lightspeed Zulus in a friends plane, and was VERY impressed. They honestly were the most comfortable headset I have ever worn (large ear cups). The ANR quality was as good as the BOSE, and the bluetooth integration feature simply outstanding!
I had heard on numerous forums, that Bose were going to release the A20 headsets at Oshkosh. They claim it features better ANR, and more comfort, and bluetooth integration!! I was quite excited, as I was going to Oshkosh, that I would buy a pair there.. hopefully cheaper and sooner availability than in Australia.
Bose had a very elaborate display set up at Oshkosh, with some very expensive advertising and lots of very good looking girls demonstrating the A20 headsets and their features. Bose had loud "aircraft type" background noise playing during the demonstration, and it was all very impressive.The headset felt the same as my old Bose, but the ANR may have been a touch better. I was disappointed that the A20 bluetooth feature does not include streaming from your mobile phone, i.e you can't wirelessly listen to music (you can with the LightSpeeds)...you have to connect a patch cable (same as the DC X11). Also the transition from music/phone to ATC/Radio override was very abrupt, with the music reverting back startlingly at full volume.. instead of a gradual increase. Also, as far as I can determine (and I am willing to be corrected), if you are receiving a phone call with the A20, a radio transmission will mute the call. The sales person claimed that you could set it so that this doesn't happen, but was unable to demonstrate how.. even after consulting with colleagues.. and the instruction book makes no mention of it!
However, I was pretty impressed with the A20 and at US$1095 I decided that I would buy a pair at the end of the week to save carting them around all week.
But then Jaba and I saw the Lightspeed stand NEXT DOOR. They had a sign out the front that invited you in to compare the Lightspeed Zulus to the new Bose A20s!!
Bugger me..they had 5 stands with both Zulu's and A20's and a really loud speaker imitating aircraft noise. There was a big line-up of people at every booth to do the comparison... and boy..what an eye opener!
Both Jaba and I, and most people there were of the opinion that the ANR and comfort of both sets were line ball. The Bose is slightly lighter in weight, but I found that the Zulus didn't squeeze my ears as much. I don't wear glasses, but a few there that did, reckoned that there was no difference in either set with glasses on. The bluetooth functionality on the Zulus is far superior to the A20. Bose have really dropped the ball with this. They can't match the features on their new product to the Zulus that have been around for about 2 years. With the Zulus, you can easily prioritise between phone/music/radio..and stream devices with bluetooth. You either can't..or can't do this easily with the Bose.
Bottom line is that the Zulus at the show special price of US$800 represent excellent value for money and are the better product overall.
As Jaba mentioned, a old pair of Lightspeed XL20 (their first ANR headset) that I have, was submerged in floodwater here recently for 2 days. After leaving them out in the sun for a week, and replacing the batteries.. they work like new (after a new set of ear cups..$10 at Oshkosh).