If it is for easy user scripting: Lua. Flexible, easy to learn,
especially designed for that purpose.
Yup. And fast. And easily mappable to a different language like
LilyPond. String or symbol? Not a choice you need to make, there are
only interned strings. List, array, hashtable, records? Not a choice
you need to make, there are only tables. And so on.
Both have in common that there is a big user base,
Lua does not have such a large user base. More like a fan base.
Python, in contrast, is solidly mainstream.