Astro and React are not competitors in the way the framing suggests - Astro renders React perfectly happily. The real question is what runs on the client by default, and the answer should follow what the page actually does.
If most of the page is content people read, start with Astro. If most of it is interface people operate, start with React. Nearly everything else is detail.
The actual difference
React ships a runtime and hydrates the page: the component tree is rebuilt in the browser so it can respond to interaction. That cost is worth paying when the page is an application.
Astro renders to HTML at build time and ships no JavaScript unless you ask for it. Interactive pieces become islands - individual components that hydrate while the rest of the page stays static HTML.
So the question is not which is better. It is what fraction of your page needs to be alive in the browser.
When Astro is the right default
Marketing sites, documentation, blogs, portfolios, content-led commerce. Anywhere the page is mostly text and images with a few interactive elements - a menu, a carousel, a form.
This site is Astro. It has a preloader, scroll animation, a slider and a contact form, and all of it is islands or plain scripts on top of static HTML. The result is thirty-odd pages that load as fast as files, because that is what they are.
The benefit compounds for SEO. Content present in the HTML needs no rendering step to be indexed, and Core Web Vitals improve mainly by not shipping JavaScript you did not need.
When React is the right default
Dashboards, editors, anything with shared client state across the whole screen, anything behind a login where SEO is irrelevant and interaction is constant.
Most of the product work in my portfolio is this shape. A dashboard where filters, charts and tables all respond to the same state is miserable to build as islands, because the islands need to talk to each other and you end up rebuilding a state layer by hand.
That is the clearest signal: if your islands need to share state, you wanted a React app.
The hybrid that usually wins
Plenty of real projects are both. A marketing site with an interactive pricing calculator. A documentation site with a live playground. Content with an application bolted on.
Astro handles this well: static pages, with the calculator as a React island hydrating on its own. You pay the React cost on the one page that needs it instead of the thirty that do not.
Going the other way - a full React app with content pages inside it - works too, but you pay the runtime everywhere to serve interactivity in one place.
What about Next.js?
Next sits between them and is the right answer more often than either extreme. Server components mean you are not automatically shipping the whole tree, and you get routing, data fetching and API routes in one framework.
My rough split: Astro for content-led sites where the interactive parts are genuinely peripheral. Next for applications with meaningful public content. Plain React for dashboards behind a login where the public side does not exist.
The failure mode to avoid is picking a framework because it is what you know and then arguing backwards. A portfolio site does not need a full application framework, and a dashboard does not want to be assembled from islands.
Questions
Is Astro faster than React?
For content-led pages, yes, because it ships no JavaScript by default while React ships a runtime and hydrates. For an interactive application the comparison stops being meaningful - you need the client runtime, and Astro would simply be rendering React anyway.
Can you use React inside Astro?
Yes. Astro renders React components, and the island model lets you hydrate individual ones while the rest of the page stays static HTML. This is usually the right answer for a content site with one or two genuinely interactive pieces.
Should I use Astro or Next.js for a business website?
Astro if the site is mostly pages people read with a few interactive elements. Next.js if there is a genuine application alongside the content - accounts, dashboards, personalised views. For a typical marketing site, Astro is lighter and ranks better for less effort.
Is Astro good for SEO?
Very. Content is in the HTML at build time so it needs no rendering to be indexed, and Core Web Vitals benefit from not shipping unnecessary JavaScript. It does not do your on-page SEO for you, but it removes the technical obstacles.