Why only choose these four? I recommend a place-Palau, an island country just south of Taiwan Province Province at 7 degrees north latitude. The water is clear and the sand is young. Although the beach is not as good as Madai and Saipan, the scenery under the sea is first-class. Palau is mainly famous for snorkeling and is the first snorkeling sanctuary in the world. National Geographic magazine has selected 50 places worth visiting in the world, and Palau ranks first in the series Paradise on Earth.
Palau's awareness in China is not high, and most tourists to Palau are Japanese and people from Taiwan Province Province.
Specific information can be found in Palau KBT Travel Agency official website, and Baidu can search for "Palau KBT Travel Agency".