Next.js vs Remix for a small SaaS
For most small SaaS products, either Next.js or Remix will work perfectly well. The differences that matter are less about speed and more about how naturally each framework fits the shape of your app.
Where Next.js tends to fit well
Next.js has a very large ecosystem, a huge amount of community content, and works well when a meaningful part of your product is public-facing content (marketing pages, blog, docs) alongside the authenticated app. If you expect to reach for a wide range of third-party integrations and want the most existing examples to copy from, that ecosystem size matters.
Where Remix tends to fit well
Remix leans heavily into web fundamentals: forms that work without client-side JavaScript, and data loading and mutations that map closely to routes. For an app that is mostly authenticated screens with a lot of forms and data mutations, that model can mean less custom plumbing to keep server and client state in sync.
The honest answer
If your team already knows one of the two, use that one. The migration cost of switching later, once you actually understand your product's real data-fetching patterns, is usually smaller than the cost of picking wrong upfront based on a comparison article. Ship the first version, then revisit if something is genuinely painful.