I believe in the majority of cases SSE are a better technology than web sockets (e.g. WS do not seem to conform to HTTP/2.0, SSE offer transparent (browser-supported) reconnects, SSE event ids allow for replay, etc). The downside is no support in IE/Edge (you can vote at https://goo.gl/bd8V1K), no binary content (but again usually JSON is enough) and no fully bidirectional communication.

A good talk at the matter can be found at https://youtu.be/NDDp7BiSad4