I need to implement a WebSocket Server, what should I use?

In one of those typical "geeks coffee breaking" we went into a discussion about a scenario where someone needs to develop today a WebSocket Server, what would be the best approach to do it? That's a great topic of conversation to be having around the coffee machine, right? Who does not love a good discussion around WebSockets Servers? Basically our discussion was started around the technology you would you advise: ASP.NET, ASP.NET Core or Self-Hosted for example in a windows service? And bringing into the picture characteristics such as Scalability and Availability? We went back and forward it those typical approaches (ASP.NET vs Self Hosted), when someone throw in the air: