I would tend to use Janet for scripts, especially ones that need to talk to the outside world because of its fast startup and batteries included standard library (particularly for messing with JSON, making HTTPS requests, parsing with PEGs, storing data in maps), while I would use guile for larger projects where things like modularity, performance, or metaprogramming were more important to me.

That being said, these days I use Clojure for both (I use babashka to run scripts: https://babashka.org/)