(I work at Stream, we power activity feeds, chat and video calling/streaming for some very large apps)

You should in most cases just use websockets with a keep-alive ping every 30 seconds or so. It's not common anymore to block websockets on firewalls, so fallback solutions like Faye/Socket.io are typically not needed anymore.

WebTransport can have lower latency. If you're sending voice data (outside of regular webrtc), or have a realtime game its something to consider.