SignalR uses .NET and languages like C#. Also, it's mostly an API on top of ASP.NET -- it needs the rest of the Microsoft web server stack.

Node.js uses JavaScript or compatible languages like TypeScript. It's a self-contained web server, but needs a library from npm to actually support websockets.

One way of looking at it: SignalR is like the "ws" package for Node.js. Node.js is to "ws" what ASP.NET is to SignalR.

If you're a developer used to .NET and used to deploying applications on Windows, using SignalR will feel comfortable.

If you're a developer used to JavaScript and used to deploying applications on Linux, use Node.js will feel comfortable.

Both can be used to build a web app with game logic. Also, you CAN deploy Node.js on Windows if you have to. But doing that is "fighting against the stream."

The development process is very different, for the obvious reason that Node.js/ws is generally a Linux ecosystem thing developing in JavaScript or TypeScript and your-favorite-editor-plus-NPM, and ASP.NET/SignalR is generally a Windows ecosystem thing developing in C# and Visual Studio.

If you're most comfortable with Visual Studio and Windows SQL Server, use ASP.NET/SignalR. If you're most comfortable with vim/npm and MySQL or Postgresql, use Node.js/ws.

For performance, there is not a big difference between the systems. (Yes, you can build a benchmark to prove anything, but the order of magnitude is the same.)