All of the authentication process now is centralized in AAD other options remains temporarily as compatibility services but they will be retired in future.
ACS is migrating to whole AAD feature.
As you can see in current azure product offerings there is no reference to ACS, even more all the ACS stuff used to be done thru the old Silverlight Azure portal and few things in the 'older' site manage.windowsazure.com.
No references about ACS in the new one
http://portal.azure.com
B2C is oriented to full current standards like OAuth and the authentication model is created to be embraced by web, mobile and desktop developers.
Azure Active Directory B2C
As you can see AAD B2C still in preview, that could be a problem, nevertheless success cases like Real Madrid could give you confidence about to embrace the technology even in early states.