For simple queries use managers, for complex ones use querysets.

manager:

• Facade for operations on the data storage
• Delegate performing the queries to querysets
• Could be used as “repositories”
• Interface that provides query operations to models (CRUD on the tables)

querysets:

• “final frontier between the domain and the raw data storage”
• Implement the “Query Object Pattern” by Martin Fowler
• Allow building queries with python objects
• whenever you need to customize how an SQL will be built or its response, querysets are where that it must be done.
• Queries are made using “lazy loading”