I've attended both. In the late 1980's, I attended ACOA meetings in the city where I lived then. I really got a lot out of them because it was the first time anyone had ever listened to me, had ever validated me. (Part of that was the zeitgeist. When I grew up there was the implied idea that the parent was always right. You didn't talk about family alcoholism, abuse, etc. If you did people looked at you like you had two heads. Nobody wanted to hear it. But I digress.)
In hindsight, the ACOA meetings I went to didn't focus much on the solution. We didn't have sponsors because the group was so new.
I have been going to Al Anon about 10 years now and it has given me much more than ACOA ever did. Of course I'm a very different person. Oh, and in my city--and the one where I used to live--ACOA meetings have faded away.