Real world considerations: MS-SQL vs PostgreSQL vs MySQL

I have a custom-built business application running on a Microsoft SQL Server database. Recently, I started thinking whether it would be feasible to migrate to a free, open-source database in order to reduce licensing costs. I began researching the differences between PostgreSQL and MySQL - specifically, which one to choose and why. All of the search results I found were fairly generic: brief historical overviews, surface-level feature comparisons, and high-level summaries. Nothing that offered concrete, practical reasons for choosing one over the other. This post aims to outline the tangible differences and key observations I encountered early in my hands-on evaluation. For PostgreSQL, I used version 18.2 with pgAdmin 4. For MySQL, I chose the MariaDB 12.2 fork, using HeidiSQL as the client tool. I’m approaching this from a practical perspective: I am both the developer and the DBA for this application and its server environment. MS SQL Server has served me well. It handles most worklo