snake_case is just more readable overall. PascalCase and/or camelCase are okay in moderation and add a kind of emphasis, which is why e.g. Rust uses PascalCase

snake_case is just more readable overall. PascalCase and/or camelCase are okay in moderation and add a kind of emphasis, which is why e.g. Rust uses PascalCase for types (other than core built-in ones) and enum case constructors. SCREAMING_SNAKE_CASE is ok for even rarer things that should stand out - C/C++ uses it for preprocessor macros, Rust for program constants and global variables. Ada_Case is rare and mostly shows up in languages with case-insensitive identifiers, like Ada itself.