I was trying to type out some kind of rebuttal, but yeah, just use Postgres with jsonb if you really need "document" behavior. Mongo is so fraught with issues that given the alternatives that exist now (CouchDB, Postgres with JsonB, etc) just avoid it.

I had good experience using for rapidly-changing map data that needs to be queried based on location. Indexing over coordinates on the surface of a sphere is supported out of the box, which makes it simple to use with relatively low latency on databases of GeoJSON documents on the order of a few terabytes, although I'll admit to not knowing if that's a feature supported out of the box on another document database.