I shall be careful what I say since most who have replied are lovees of BASC.
None of them are any good except at the small stuff, and its certainly not a case of you get what you pay for. Even the Police are unimpressed (mentioned by another member).
If, like most people you want value for money, given the political influence is derisory, then i would go with SACS or NGO. - both carry equivalent insurance but neither claim to be able to 'control' the Police or parliament.
I would, as would many, favour a single organisation and then a mandatory membership. We simply do not have one organisation which stands up for us effectively, so whilst wishing to support some group which could stand our corner on the environment and the many issues we face, I don't believe there is a single effective organisation. I wont pay for something because it calls itself, erroneously, the Voice of Shooting or because others regard it as the best of a bad bunch - wrongly.
Too many issues have tripped us over the last number of years, if you are honest you will know what they were and acknowledge they were gross failings. I wont pay for gross failings, even if I want a strong organisation to speak on shootings behalf. I therefore buy just insurance and will continue to until there are no major fails for a number of years . If there were any sugnificant successes I would probably rejoin the day after.