I second A & C.
I represented the interests of our Pilots with the IPA in a company that is now no more. The IPA in my opinion were not a lot of help.
I was a member of BALPA for many years and for a very short time a company rep. BALPA were a much more effective association in our airline, a big British one it must be said.
To sum up: I would have to say that with my experience of both, and in completely different airlines, I would put my money with BALPA.