PFX and Bose A20 are the premier headsets at the moment. Comfort is key when it comes to a headset. There are people who swear the A20 is more comfortable, and those that swear by the PFX. Both groups are correct, as comfort depends on the person.
The PFX has some really advanced features. If you have an iOS device to connect to it, there are a lot of customizable settings. The PFX likely has the more effective noise-cancellation, but that's based on anecdotal evidence. I feel like the build quality is better on the PFX than it is on the A20, but that's also anecdotal. One of the great things about Lightspeed is they have outstanding customer service.
The A20 has a smaller control module (the PFX control module is substantial), and uses far less battery power. You can use the A20 to make bluetooth calls from your phone, but you can't listen to music with Bluetooth, you have to run a cable to it. The PFX does both (BT calls and BT music).
The best thing really is to try to get your hands on both and see which is more comfortable for you, which sounds better to you, and which has features you appreciate more.
There are some other heads out there that are worth taking a look at, like the Zulu 2, the Quiet Technologies Halo, and a few others.
Personally, I use a QT Halo for airplanes, and I absolutely love it for that. For helicopters I use a headset from a small, custom headset company that I'm not very happy with.