I'm not GP, but for me that would be TypeScript. TypeScript's tooling is as good as Go's across the board, it's very readable, it's a simple language, it has very few footguns, and it compiles fast. But it has better type safety than Go.

This isn't an exhaustive proof as no language will every be fully Pareto optimal in practice (it's just not possible, there are too many dimensions), but I'd argue it's at least somewhat close.