Hi @billy2,
There is no preferred method over the other, this all depends on the complexity of your use case. The more straightforward way would be using a Post-Login Action if you just need to export the basic user information from the registration process and want to keep things a bit simpler.
Otherwise, if your intent is a more complex automatic user export you can also rely on creating Event Streams using a custom webhook ( currently in Early Access ), which covers user provisioning, as well as updating or deleting them. This will require more work, given that the trigger is asynchronous, so I would recommend checking out the Events Best Practices, as well as this blog post - Discover User Lifecycle Changes via Event Streams.
Thanks,
Remus