At our airline, we have T & G and CC89; couldn't say which one was more popular, although the majority of people on my training course chose to sign up with CC89.
Haven't joined a union yet, although open to being convinced of the benefits. I think it would help if either of the above could produce a catalogue of instances in which membership of one union or the other worked to the member's advantage.
So far, only the offer of free legal advice looks vaguely interesting.