I do like USSA but they did remove all references to multihulls out of their new small boat learn to sail book. They do good work but unfortunately I have seen their negative multihull biases over and over.

ASA I am not sure is much better because their attitude is if you want to be a good sailor you must sail a monohull first before a multihull... Look how their certification system is set up. No way to get certified on a cruising multihull unless you take a monohull class. However with this new venture maybe things are changing.