Not OP but, in my mind (having used both extensively), Postgres is basically the closest I feel you can get to MSSQL in the open source world, in terms of compl

Not OP but, in my mind (having used both extensively), Postgres is basically the closest I feel you can get to MSSQL in the open source world, in terms of completeness of a fully functional relational database that scales - not to mention Postgres has tons of features that MSSQL has been playing catch up with for years. I like both of them personally. Postgres didn't used to have as strong of a showing on Windows, and not as fancy tools as Management Studio/Query Analyzer/Azure Data Studio, but I think today Postgres is absolutely viable to replace SQL Server if you want to switch to open source.