Which vector database should you choose for a startup RAG prototype?

Choose pgvector if you already use PostgreSQL, since it adds vector search with zero new infrastructure and handles millions of vectors adequately. Choose Pinecone serverless for the fastest zero-ops setup with a generous free tier and no servers to manage. Choose Qdrant or Weaviate Cloud if you want open-source underneath with a managed experience and easy migration to self-hosting later. Avoid Milvus for small prototypes since its multi-component architecture is overkill until you reach tens of millions of vectors.