I appreciate the answers. For others reading, I also just ran across another thread where you posted relevant info [0]. In the case of my game, I'm going to consider SSE, since most of the communication is server to client. That said, I already have reconnects etc implemented.

In my research I recall some potential tradeoffs with SSE [1], but even there I concluded they were minor enough to consider SSE vs WS a wash[2] even for my uses. Looking back at my bookmarks, I see that you were present in the threads I was reading, how cool. A couple WS advantages I am now recalling:

SSE is one-way, so for situations with lots of client-sent data, a second connection will have to be opened (with overhead). I think this came up for me since if a player is sending many events per second, you end up needing WS. I guess you're saying to use UDP, which makes sense, but has its own downsides (firewalls, WebRTC, WebTransport not ready).

Compression in SSE would be negotiated during the initial connection, I have to assume, so it wouldn't be possible to switch modes or mix in pre-compressed binary data without reconnecting or base64-ing binary. (My game sends a mix of custom binary data, JSON, and gzipped data which the browser can decompress natively.)

Edit: Another thing I'm remembering now is order of events. Because WS is a single connection and data stream, it avoids network related race conditions; data is sent and received in the programmatically defined sequence.

0: https://news.ycombinator.com/item?id=43657717

1: https://rxdb.info/articles/websockets-sse-polling-webrtc-web...

2: https://www.timeplus.com/post/websocket-vs-sse