First make sure you have clearly defined the set of activities you would like to assess. The CSAT assesses the sustainability capacity of a clinical practice, such as a mental health screening procedure or a hand hygiene process. The PSAT assesses a wide range of programs in public health and other fields (e.g., social services and education), such as a healthy school lunch initiative or an adult literacy program.
If you are still unsure of which tool to use, you can read about and compare the CSAT domains and the PSAT domains. You can also preview the CSAT questions and the PSAT questions. Think about how the domains and questions apply to the set of activities you would like to assess. One tool may stand out as more useful for your purposes.