I'll be fairly blunt here, list exactly what I want in descending order of importance. 
 
1. Extremely comfortable for extended use. I might go on a 24 marathon, and the headphones have to keep up!
 
2. Good noise isolation. I'm not too fussed about noise cancellation, but that would be a bonus (I expect I'll use these cans for flights)
 
3. Decent audio quality, of course. I don't want over-powered bass, I listen mainly to classical and heavy/death metal. I want to hear those symbols and guitar riffs! (Can't have the bass too light, as I said, I want to use it for films and TV too.)
 
4. Wireless (with no delay, as far as I know, Kleer 2.4GHz has no delay. Like on the Sennheiser RS170s.), however, with an optional 3.5mm port on the cans for use on planes/on-the-go.
 
As for price range, I'd rather stay on the lower side of $300/£200, and really don't care if there is a perfect one for £5. It's all about quality, not price.
 
From what I saw, the Sennheiser RS170s were all but perfect. I do need there to be the option to use it wired as well for plane journeys and on-the-go. (If I'm missing something, and it actually does, tell me soon and this is a very short thread!)
 
All help appreciated
 
Thanks
Plas