Relational workhorse vs document database.
| Postgres | MongoDB | |
|---|---|---|
| Model | Relational + JSONB | Document |
| Query | SQL | Mongo query language |
| Transactions | Strong | Good (multi-document) |
| Ecosystem | Vast | Large |
Structured data, relations, SQL expertise, almost always the default.
Document-shaped data, schema-less workflows, rapid schema changes.
Postgres by default. MongoDB when document is a genuinely better fit (rare but real).