I've never taught the Advanced course but have the ERC.
This is the MSF link describing the different courses they have available:
http://www.msf-usa.org/index_new.cfm?pagename=ridercourse info&content=C55DBB87-A0CC-53D5-64D098C9870C8030&referer=MSF RiderCourses
The ERC is the one with no classroom (well, one version has an "informal classroom", the ones I've taught were "skills practice" only). The Advanced course is described as having actual classroom time.
I'd recommend the newer Advanced class. My bet would be that the MSF has put a lot of work into it and integrated new things the ERC doesn't have. Even if it's just better teaching techniques.
And hopefully you won't mind my pointing out, if you don't practice what you learn, in any class you take, the skills will diminish over time. They are all "learned" skills.
It's not like "I passed, I'm good to go". Not even close actually. I think that's one of the biggest challenges us motorcyclists face, because we take these skills for granted with our cars / trucks. But emergency braking and swerving, along with cornering are very very different on a bike, and unless practiced regularly there's no way you can be competent at them.
Hope that helps and isn't over bearing
Oh and certainly what others have said, if you haven't taken the BRC that is definitely where I would start, they don't cover much of that material later, it's assumed you have taken that course first.