Out of the pretty small number of database systems I’ve used:
Postgres: Pretty standard choice, can’t go wrong with it
MySQL/MariaDB: Also very safe choice, I feel like it’s more feature rich than Postgres but I’m not sure
Oracle: It reeks of proprietary bloat and it’s unnecessarily different than the previous two in some things, but you can get some official enteprise support if you’re a company
Influx: It solves a specific problem (time series) but it’s very cool, modern and with api support for many languages
Out of the pretty small number of database systems I’ve used: