drupal on postgresql vs mysql vs mariadb
The occasional issue you can hit, is that a contrib module is either just badly written because the author didn't know better, or, more rare, deliberately used mysql specific functionality for some reason, meaning that the module simply won't work on your site.

I've only had this on a single occasion though, and it caused issues during installation. A quick hack of the modules install file, and everything worked out well from there on.

It's unlikely to be much of an issue, and I'm myself running some personal things on postgresql just get familiar with it.

Drupal doesn't care if you use mysql or mariadb. They're the same thing to Drupal.