I prefer NodeJS. We never know when M$ will deprecate something and bring in something new. NodeJS has more than one way to do things - Express, Koa for servers, SocketJS for real-time, etc. Whereas .NET Core, we get one of everything mostly from Microsoft developers.
Dávid Paksy
Senior Software Engineer @AdNovum at work, father of 2 kids at home.
I think - as for most question in IT - it depends. Which tech stack do you / your team know better - this already is an advantage. For some kind of applications Node seems to be a better choice.
It is also important to understand what you gain with one tech and what you give up For this, I really liked this article which explains why it is important to know what you gave up with choosing a particular technology: simplethread.com/was-mongodb-ever-the-right-choice
Many technologies can be reasonably evaluated by asking just two main questions: