To be clear: You can learn in coastal cities in China, at dive sites in Southeast Asia, and in local pools. No single option is automatically right. What determines how well you learn is not the island scenery, but whether the instructor has a current, valid teaching qualification and whether the course teaches rescue and the buddy system.
Why does location matter less? Most of an entry-level course—breathing preparation (never hyperventilate, it removes your body's only warning sign of low oxygen), equalization, static apnea (STA), and rescue procedures—can be completed in a pool; the few open-water dives can also be done in many coastal cities in China. What really sets courses apart is instructor quality and class size.
- In China: most time-efficient. Pools in Hainan, Guangdong, and other coastal areas, as well as in many inland cities, offer courses. They are suitable for building a foundation first, and you can go on weekends.
- Southeast Asia: good value. The Philippines, Thailand, and Indonesia have a dense cluster of dive shops. Courses plus accommodation are often cheaper than a trip in China, and you can also enjoy a holiday.
- Ask three things before signing up. Is the instructor's certification currently valid? Does the course include open-water dives? Does it include BO recognition and rescue? If any one is missing, choose another shop.
In short: Check the instructor and course structure first, then decide on flights. After the course, don't rush into the water alone; practice only once you can find a buddy. This one point is more practical than any certification.