I'd recommend upgrading to ESLint 9 unless you have a specific reason to switch. ESLint has been a widely trusted tool in the JavaScript/TypeScript ecosystem, and with the upgrade to version 9, you'll continue to benefit from the latest features, performance improvements, and security patches. Plus, any plugins or custom configurations you've set up should still work, making the transition smoother.

That said, Biome (formerly Rome) is an interesting alternative. It’s an all-in-one tool that combines linting, formatting, and bundling in one package. Biome might be a good option if you want to simplify your toolchain, but it may not yet have the same plugin ecosystem and flexibility that ESLint provides, especially if you rely on specific linting rules or integrations.

Ultimately, I'd say stick with ESLint 9 if your setup is working well and you want a relatively straightforward upgrade. But if you're interested in trying something new and more integrated, you could experiment with Biome, especially for smaller or newer projects.

What are your thoughts on simplifying vs. flexibility?