Which Ensign should I fly?

I will be sailing a vessel that is registered in both the U.S. Virgin Islands and on the British Small Ships Register. I intend to take her into the Spanish Virgin Islands and the BVI.

While I am in the USVI, does anyone know whether I should be flying a Red Ensign with a USVI courtesy pennant, flying the Stars and Stripes or the USVI flag?

When in either of the other two jurisdictions, obviously I need the appropriate courtesy pennant but which ensign?

Any advice gratefully received