What's the difference between RxJS and rx-node?
Why shouldn't I just use RxJS instead of rx-node in my NodeJS project?
The rx-node repository covers this in its first line:
This project provides Reactive Extensions for JavaScript (RxJS) bindings for Node.js and io.js to abstract over the EventEmitter, Streams and more.
RxJS is the official repository. rx-node adds support for a few node specific things, the details of which are outlined on their documentation page.
If you need those features, use rx-node. If not, use RxJS. Since the former extends the latter, the migration path would be fairly trivial if you change your mind later.