I'm a member of both PFA and AOPA UK. They do very different jobs.
The biggest sin AOPA UK are guilty of is a failure to adequately explain what they do. "News from AOPA" in Pilot Magazine goes a little way toward redressing the balance.
Sitting in committee in Europe is sadly becoming more and more important and I don't think anyone does a better job of that on your behalf (whether you're a member or not) than AOPA UK.
If you look at the thread referred to above, particularly the post at the top of
this page and my reply below it you'll see why there is the huge disparity in membership costs between AOPA US and AOPA UK.
If you look at
this page you'll see where the membership fees go in terms of European representation.
Here's a quote for you
In 1964 IAOPA was accepted as the sole general aviation observer to ICAO proceedings, a distinction the organization maintains to this day. In addition to regular participation at ICAO headquarters and regional meetings, IAOPA represents the interests of general aviation in the European Union, Eurocontrol, European Civil Aviation Conference and Joint Aviation Authorities.
As has been said earlier in this thread, AOPA is the organisation the regulators tend to pay heed to.
There's a discussion forum at
www.joinaopa.com please join in!