can't tell about the noise levels in most FW singles yet, but ANR is a way to go for helis.
Disadvantage of DC headset is that they just stick in ANR bits into their original headsets. Ie chunky. I used few worn out cheap passive DCs provided by school, had enough. Then I borrowed older Sennheiser headset, it was better, though still not good enough.
Still had problems with ATC clarity and the noise from cockpit that gets through other pilot's mike (student/instructor) or in general is too much for comfort.
You'd probably find most of the headsets used/bought are DC. But then, they do have dozens of models at various prices, not just passive or ANR. So one can buy higher quality passive headset.
I 'had to' go for Bose X as it's 'a standard' amongst heli pilots I see around (maybe 80-90% of those who do RW CPL/CFI or instruct at my school). As one guy said: "Bose X is good enough." I asked whether he was slagging them. He added that he had meant
"If it's good enough for the best, it's good enough for me" 
Don't forget, there's also those earplugs one can put inside DC headset. I saw it twice. Some improvement for radio clarity etc. One student said that it's comparable to Bose X if these used in DC..
Some say, get good headset once for years to come. Others, what if you don't keep on flying, or that you don't need to 'treat yourself' when doing PPL.. Then, your hearing is of high value, so treat it nicely.
Guess it all boils down to what a guy/gal feels like spending vs feeling good in cockpit.
EDIT Ask folks around to let you try different ones and their comparison.
Geez. Just found Bose X price in the UK. 750 quid?? Hmm. US=995 bucks
one UK pilot supplies website has bunch of ANR headsets priced around 300. Anyone got good experience with one of them?
Type ANR headset in search and you'd find some threads about..