I went to Transair Pilot Shop in Central London last Wednesday and tried out their range of headsets on their intercom system. In the end, it came down to choosing either the David Clarke 13.4 passive or the Pilot Communication 17-79 ANR set for £329. In the end I chose the latter.
I would recommend if your budget could stretch, then seriously consider an ANR set. I still can't believe how quiet this set is; for once I can clearly hear my Instructor and the radio.
I personally think that David Clarke sets are overrated. My conclusion after trying out a dozen or so other brands is that there are plenty of other brands that are just as good, if not, better and at the same time costing much less.
Do not buy a headset because of a particular brand; buy one that is well made, comfortable and at the same time affordable.