We use the ANR Bose Aviation X headset in both A109 and Gazelle. When compared to the passive David Clarks and Peltors (can't remember the model no.s) they replaced they are superb. Yes they are pricey, but you get what you pay for. The installed versions are less hassle because you don't have to replace any batteries (but this type probably won't suit you if you are aircraft-hopping). They are comfortable, rugged, the boom mic is easy to locate and overall, in my opinion, just about the best on the market.
God only gave you one set of ears - pay the extra and look after them.
We got ours from Alec at RGV Aviation at Gloucester; very freindly, helpful, reliable and reasonably well priced compared to the competition. We've had 7 sets from them now and have been using them for a couple of years without problem. J