Verdicts

Next.js 16.3.4 if the app is mostly logged-in screens: server components, the largest hiring pool, and Turbopack on by default for both dev and build. Astro 7.3.1 if most pages are content and only a few islands are interactive, because it ships no JS for the rest. SvelteKit 2.70.3 is the smallest runtime of the three, but v3 is in prerelease and rewrites the adapter API, so custom adapters will need work.

Fumadocs 16.15.8 if the docs live inside an existing Next.js app, because it is Next.js components rather than a separate site and you share the layout, the fonts, and the deploy. Starlight 0.42.0 if the docs are their own site: Astro ships almost no JS, and i18n, search, and the sidebar are configuration. Docusaurus 3.10.2 is the safe institutional choice with the deepest plugin and versioning story.