PostgreSQL

Its a really great product that has rich features which are well suited for our needs. It also has a NoSQL option which could be useful in some cases. And most importantly it's free to use which is always great.
There's still room for improvement though, for example, the installation and upgrade process could be made easier, online resources could be improved as well.

AWS, Heroku, and Digital Ocean all provide Postgres-as-a-service, where you pretty much never need to administrate it yourself but they do it for you. The Postgres community also has developed awesome and reasonably priced extensions, such as Citus DB and CockroachDB in case you need additional support for running it. If you need documentation, Postgres's docs are super thorough and their official forms are active.

Most of the time, the community support is enough. Their documentation is thorough, stack overflow is often enough to answer any question that comes up.

Community support is amazing and purchased support is available if required.

I am split between somewhere 6 and 8 so I gave it a 7 largely because the support is via a user community if you are on the freeware version, which entitles you no guarantee in time or quality of support, but most of the quirks are well described with numerous remedies possible. When PostgreSQL comes from for-profit vendors, say MemSQL or Citus, the support situation goes multiple notches up because they want to ensure your success. In AWS as RDS the support it a tad anemic, but works.

Easy, quick, to the point support