I like the simplistic view of MySQL to build custom queries and things like that as compared to SQL Server, which seems more cluttered.
SQL Server has a query analyzer. MySQL pretty much does the same, and performance-wise, it has less overhead for connecting to our ERP system. It seems more responsive and cleaner. With MySQL, you get what you need without any overbloating, for which Microsoft is known. That's why they have so many constant security patches for everything because there is so much stuff, which degrades performance.