My last two projects have been developed with RethinkDB as the backend, and personally I love it. I tried playing with Mongo for a bunch of projects, and I just didn't enjoy it's shortcomings. Coming from years of MySQL, and other relational databases, RethinkDB gives me the best of both worlds. A relational query language, with the flexibility of schema less tables. Change feeds make real time applications super easy, and the admin GUI is awesome. It's essentially the next evolution of databases, developed by people who know what they are doing. You'll also definitely want to grab Thinky.io ORM when working in Node.js