I like thinking about the best tools for the job, or "jobs to be done" as Clay Christensen would put it. But why wouldn't you use MongoDB for things that require ACID? MongoDB has had cross-collection ACID transactions since 4.0 (years ago) and in-collection transactions (less useful, of course) since a long time before that. PostgreSQL is indeed a pretty awesome database. That said, the JSON support is just so very painful. It's nice that it supports indexes on JSON, though, once you get through the syntax. Thanks for your post.