which transition strategy works the best?

When IPv6 is deployed by a Service Provider to bring on an IPv6 Enterprise, which transition strategy works the best?

A.
Deploy IPv6 at the Edges and tunnel Enterprise through the core

B.
Deploy IPv6 at Edges and Core at the same time for smooth transition

C.
Deploy IPv6 at the core first and then move to Edges toward the end customer

D.
None of the above will work