Which DB would be better with NodeJS?

Question

I've two option, first one is Mongo and second is Mysql

Answer 1

depends what you want to do. Mongo is a NoSql database. Your data is saved in JSON format. It can vary the data definition in a more flexible way.
MySql, is a relational database. You must define your tables carefully before to start.

Answer 2

Mongo is more flexible because it's Nosql, no schema database and in JSON format.
Almost anything you can do in Mysql can be achieved when using Mongo db.

Since it's Nodejs, I'll suggest Mongo db because they're close and you probably knows how to access object properties.

If need arise to modify your database, in Mongo you're free to alter any collection(referred to as table in Mysql) anytime. I'm sure you'll be happy to work with Mongo db.