Postgres or Vertica CE depending on the use case. The Postgres column store extensions get better every day, making Vertica CE less attractive. Redshift is great, but it's still missing some stuff like copy from STDIN that makes I/O difficult and restricts interoperability with Postgres. I don't always love Vertica and it's too expensive if you're not running CE, but being able to start a project in a small Postgres instance and then migrate seamlessly to Vertica when you need is very useful sometimes.
There is no reason to use Mongo unless your data is JSON or really fits the JSON flexible schema use case. Loading tabular or well-dimensioned data into Mongo is a huge mistake.
