I am an ASCAP member, both as a performer and as a publisher. They have a great website and the services offered through the site are good. You can sort out all you need to know to register your publishing entity and your works.

I looked at BMI too. Many Celtic and Folk performers use BMI, but many are ASCAP members. I chose ASCAP because they seemed to have a broader industry footprint, they've been a big player for a very long time and they had the services I needed. As far as I know, ASCAP and BMI are the big guys in the industry and that can be an important factor. I want my published works to be available to multiple media outlets; radio, tv, film and recently MP3 services. ASCAP seemed to me to be most flexible in this regard.

I have been a member since 2000. I think they are a good choice.