Just about everything. From the typical piston singles to the Extra 300 to light twins to the Gulfstream 450. Not too long ago I used my Bose A20 with an adapter in a Robinson R22. In the summer that is my typical configuration just about every practical test I conduct and they work just fine in that application, in my experience. That is the exact opposite of my experience, although I wouldn't say the Lightspeed ANR is "worse," in fact it is somewhat comparable but not quite as good as the Bose. Rather, my chief complaint is simply the ruggedness of the Lightspeed models. A very common problem from what I've gathered. I owned a Pitts Special S-2C years ago and it was pre-Zulu era (I had the 25XLs.) Actually that was the application which moved me to the Bose X (no A20 at the time.) A much better, quieter headset, especially in the Pitts Special. I was flying an Extra 300 recently and let the other guy try my Bose A20. He was using David Clarks with a strap. He said he was going to order a pair. I'm not doubting your experience, but I have a mountain of time with both of these headsets in just about anything with wings or rotor blades, and I'm absolutely convinced that Bose's A20 model is the best civil aviation headset ever built. Comfort is entirely subjective, so I have no doubt that either might be perceived as "more comfortable" than the other by a given user. But in terms of reliability, functionality, sound quality and ANR, Bose simply wins.