Polling options

There's a fair few ways of getting 'real-time' data, namely:

Short Polling - Client makes HTTP requests to the server at regular intervals (1-2s). Has a high overhead, but the data is decently quick (but still not real-time).
Long Polling - Unlike Short Polling, doesn't work on intervals. A request is made and remains open until a response is found (or a timeout occurs).
Websockets - A persistent two-way connection. Real-time.
SSE - Server to client only. Also real-time.