Replication or Standby?

Hope you are aware that even your replication option also works on database links. The difference is the data in HQ will not be real time if you use replication option and readonly snapshots. Your data will be real time only when you have synchronous bidirectional replication, which is not an option as you have lots of resolution conflicts to deal with.

This is what I understood from you saying real time data availability at HQ.

For auditing, my suggestion is standby. much less overhead and maintenance work.