SML is a nice language with a cleaner syntax and is standardized. Still, my answer would be OCaml without questions. It has better tooling, better performance,

SML is a nice language with a cleaner syntax and is standardized. Still, my answer would be OCaml without questions. It has better tooling, better performance, a larger community, a larger ecosystem, more features and more work being done on it with basically no downsides.