[Gaelan]

I haven't used Nuxt, but I've used both Next and Gatsby a bit.

The biggest difference is that Gatsby is exclusively static, whereas Next can do static pages, server-rendered pages, or a hybrid of the two approaches.

Gatsby has a GraphQL-based data-fetching system, while Next is much less opinionated. Next gives you a place to do your data fetching, but doesn't dictate how you fetch it. Personally I find Gatsby's GraphQL stuff confusing, but YMMV.