As others have said, there are lots of choices; BASC, SACS, NGO, CA etc etc
For me it is BASC all the way. The policy is clearer, there is more back-up, the guys in their specialist depts are very very helpfull, especially on the firearms front, and as has been said they have more teeth and clout than the others when it comes to arguing your corner.
There have been cases of then not helping in some cases. But its worth noting they are a Members organisation, they help their members, not those who are not members. In legal cases, they will offer advice, the best advice, but (I believe)