Comment by stevebmark

SSR by default, and then if you want, client side hydration and navigation so subsequent page loads happen in the client. However, the size difference between an HTML response and a JSON response is negligible, and HTML responses don't have to wait for Javascript to download, parse, execute, kick off off a request over the internet, get the data back, execute the result, and update the DOM. Browsers have literally decades of optimization to show HTML to users as fast as possible, and doing this in Javascript is fundamentally slower.