"SQL or NoSQL?" used to start long arguments. In 2026 the data points to a clear default, with a few real exceptions.
The 30-second version:
Adoption
In the 2025 Stack Overflow survey, roughly 45% of developers used PostgreSQL against about 25% for MongoDB. Adoption isn't everything, but it means more hiring options, more tooling and more answers when something breaks at 2 AM. Current versions are PostgreSQL 17 and MongoDB 8.
Transactions and correctness
Full ACID compliance is a core design principle of PostgreSQL. MongoDB has supported multi-document ACID transactions since version 4.0, so "Mongo can't do transactions" is outdated. It's still not the shape the database was built around.
Scaling
MongoDB's native sharding is a genuine strength when you need horizontal scale with heavy write throughput. PostgreSQL scales out with read replicas, partitioning, or extensions like Citus. It works, but you assemble more of it yourself.
So which one?
PostgreSQL is the stronger default for most applications. Choose MongoDB when your data is genuinely schema-less and document-shaped, and you need high write throughput with horizontal scale from day one.
The full comparison, scores and FAQ: MongoDB vs PostgreSQL — full breakdown.
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