* Pinyin: This is the official system used in mainland China, Singapore, and other countries. It is the most widely used system and is generally considered the easiest to learn.
* Wade-Giles: This was the standard system used in the West until the 1980s. It is still occasionally used in some older materials but is less common today.
* Yale Romanization: Developed by the Yale University in the 1940s, it is mainly used in linguistics and for specific dialects.
* Gwoyeu Romatzyh: This system was developed in Taiwan and is based on the pronunciation of Mandarin Chinese. It is still used in Taiwan, but less commonly than Pinyin.
* Other systems: There are many other systems that have been developed throughout history, but these are not widely used today.
The choice of which system to use depends on the context. Pinyin is the most common and versatile system, while others might be used for historical reasons or specific applications.