nopCommerce officially supports multiple database systems, including:
MS SQL Server（or MSSQL (Express)）: Versions 2012 or above.
MySQL: Versions 5.7 or above, with support starting from nopCommerce 4.30.
PostgreSQL: Versions 9.5 or above, with support starting from nopCommerce 4.40.
MS SQL vs MySQL vs PostgreSQL
both PostgreSQL and MySQL are supported as database options for nopCommerce, provided the specific version requirements are met.
Nop-Templates, a provider of nopCommerce themes and plugins, also confirms support for these databases, noting a specific exception for their Ajax Filters plugin which does not support PostgreSQL but does support MySQL and MSSQL.
MSSQL
MSSQL would have the best as its native and been around the longest.
MySQL
PostgreSQL
We're working on a MSSQL to PostgreSQL migration right now for our Linux deployments. We choose PostgreSQL for performance and scalability over MySQL. We'll find out if that's true. PostgreSQL wants all object names to be in lowercase, so that's been an issue.