I don't know, I got started with Mongo because ... it was so easy to start with, but come deployment time got bitten by a LOT of issues (which essentially negated any advantage in using Mongo).
As a result of this experience I almost exclusively use PostgreSQL, and I've never EVER been burned by taking this approach.
Sometimes I do use another DB but there has to be a seriously good reason for it.
Same thing. I was a software dev, then I went to the back end with MongoDB and NodeJS, and I learnt what ACID means...
Also about MySQL, many people forget it isn't ACID compliant either and just look at benchmarks or use MySQL "because Facebook uses it". I am sure that if any startup would use PostgreSQL it would avoid many problems on the road.
As a result of this experience I almost exclusively use PostgreSQL, and I've never EVER been burned by taking this approach.
Sometimes I do use another DB but there has to be a seriously good reason for it.