Mongodb vs Postgres in a Nodejs App

Mongodb vs Postgres in a Nodejs App

I'm building a nodejs application and am utterly torn between nosql
mongodb vs rmds PostregresSql. My project is to create a open source
example project for logging visitors and displaying visitor statistics in
real time on a webpage using nodejs. I was planning on using mongodb at
first, because lot of nodejs examples and tutorials, albiet mostly older
ones, used it and paas hosters with a free teir are abounding. However, I
was seeing a lot of bashing on mongodb recently and found that people who
tried to use mongodb ended up switching to postgres.
http://blog.engineering.kiip.me/post/20988881092/a-year-with-mongodb
http://dieswaytoofast.blogspot.com/2012/09/mysql-vs-postgres-vs-mongodb.html
http://www.plotprojects.com/why-we-use-postgresql-and-slick/ I also a fan
of heroku and have heard a lot about postgress becuase of that and find
that sql queries can be nice sometimes.
I'm not a database expert, so I can't tell for the life of me which way to
go. I would really apreaciate it if you could give some advice on which
one to consider and why.
I have a few criteria:
Since I want this to be a example, it would be nice to have a way to host
a decently sized amount of data. I know that mongodb defiantly offers
this, but postgres paas like heroku seem to have pretty small
databases(since I am logging every visitor to the website)
A database that is simplistic and easy to explain to others.
Performance doesn't really matter, but speed can't hurt
Thanks for all of the help!
Note: Please no flame wars, everyone has their own opinion :)