I have a David Clark set, think its garbage... the active part is pretty sketchy in how active it wants to be (it cuts in and out of activeness-ness), the volume with ANR on is lower than a non ANR headset (which I guess would work if the ANR actually was worth a !!!!), the battery box is in a pretty awkward position and is pretty big, battery didn't last super long, everyone I know with em has lost the battery box cover, etc. Works good as a backup and lend out set, but I don't even bother with the active switch... causes more of a headache than 5 radios at once gives you already. Without it switched on its a oversized set of normal DKs.
I hear the Sennheiser ones are pretty slick too, hell I have a pair of their studio monitor music headphones here and they are the cats ass, so I'd assume their aviation line is good.
Mike