Choose Havelock over extra Port Blair sightseeing when your main reason is beach time. In Port Blair, you get the airport link, Cellular Jail, short city stops, and return access. In Havelock, you get Radhanagar Beach, Elephant Beach, diving, kayaking, and a slower stay. If you prefer museums, history, and less ferry movement, take more Port Blair time. If you want sand, sunset, and water activities, keep two nights in Havelock.