I had to make a similar choice last week en route LGW to Caribbean. Cab manager had advised that we had a sick passenger (terminally ill with cancer) whose condition was worsening. We were an hour past the Azores. A doctor on board recommended expeditious landing so we turned back. We asked Sta Maria which Azores airfield was better as far as medical facilities were concerned and they suggested Lajes was preferable to Sta Maria, so that's where we went.