If SQL Server Express satisfies your needs without running its limitations, and your developers / admins are best acquainted with MS SQL, then use it.
Otherwise use MySQL.
In these situations, a comprehensive strategy usually uses what you know as long as it meets your technical needs.
Limitations of SQL Server Express:
- Limited to one processor at a time (although it can use all the cores of a multi-core processor)
- Can use a maximum of 1 GB of RAM to buffer data.
- Maximum database data size 4 GB (10 GB in 2012)
- SQL Profiler is not included (but can be used with inexpensive publisher tools)
- No Work Planning (IIRC)
Import / Export Not Provided (IIRC)
SQL Server Express - , , .