recommend Thailand, especially those islands, big and small PP, Koh Samui and Phuket.
Indonesia is not recommended for historical reasons. Although it has beautiful scenery such as Bali, the massacre of Chinese people in that year is still unforgettable.
In Malaysia, the scenery is actually good, but the playability is not strong. Generally, people visit artificial landscapes such as Genting Casino, but there are not many recreational activities such as diving.
to sum up, Thailand is recommended. Thailand tourism recommends a deep tour of Phuket, sharing a speedboat to play on several small islands near Phuket, and diving in the legendary paradise swimming pool.