SQL Server vs MySQL

SQL Server and MySQL are free.

SQL Server

Free

Microsoft’s relational database. The usual pair with C# and Azure.

Pros of SQL Server

Natural pair with C#
Strong Azure tooling
Express is free to start

Cons of SQL Server

Paid editions get expensive
Less common outside Microsoft shops

MySQL

Free

The relational database behind a huge share of web apps and WordPress.

Pros of MySQL

Easy to find hosting
Familiar SQL
Free Community edition

Cons of MySQL

Fewer advanced features than Postgres
Oracle steers the project