PostgreSQL
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Adopt
Our preferred relational database is (and has been for many years) PostgreSQL. We prefer it over cloud-vendor specific relational databases. In our projects we experienced several shortcomings in such cloud-vendor specific relational databases and we see no advantages in using them over PostgreSQL.
AWS as well as DBaaS providers support PostgreSQL (or are compatible with it). When on AWS it may be that Amazon Aurora PostgreSQL may be a preferred choice over Amazon RDS for PostgreSQL depending on your (business) requirements. Please see Is Amazon RDS for PostgreSQL or Amazon Aurora PostgreSQL a better choice for me? for more details.