The only time I would recommend Mongo is for storing geo-spatial data, as it has several built ins that make it much easier to work with. Even then I find it a lot more convenient to keep that data in Postgres and replicate it to Mongo.
Hm, fast bulk write is an area where PostgreSQL generally handily beats MongoDB. I do not see why it would be different for geodata. MongoDB beats PostgreSQL for some things, but not bulk load.
