As of January 2021:
pyodbc is under active — though somewhat sporatic — development, is officially supported by Microsoft (when using the current version of Microsoft's ODBC Driver for SQL Server), and has a couple of Microsoft employees contributing bug fixes and new features that relate to accessing SQL Server and Azure SQL.
pypyodbc came along after pyodbc but is not "the newer version of Pyodbc", it is an alternative pure-Python implementation. It has not seen an official release since January 2017.
pymssql lost a lot of momentum and was discontinued in November 2019. Since then a couple of contributors have stepped up to keep the project going and there was even an official release in September 2020.
However, pypyodbc and pymssql still lack some features available to users of pyodbc, particularly the fast_executemany feature to improve the performance of bulk inserts. pymssql can also be difficult to configure for secure connections (e.g., as required by Azure SQL), especially on Windows clients.
