I'm not familiar enough with the current space. But my preference would be something like: plain old server side rendered HTML with JS that enhances the site,

I'm not familiar enough with the current space. But my preference would be something like: plain old server side rendered HTML with JS that enhances the site, adds some dynamicity etc. But in which a link or button-click usually is just fetching a new page over the wire. This JS can (also) fetch data over the wire, websockets or such. And I wouldn't even expect it to be some fancy "progressive enhancement" - fine if the web-app doens't work without JS for me.