They are mostly JITs or have specific purposes (like stackless python). JITs like pypy have a raw performance advantage. But implementation is more complex, an

They are mostly JITs or have specific purposes (like stackless python). JITs like pypy have a raw performance advantage. But implementation is more complex, and there is startup time overhead. Also I have heard CPython reference implementation prefers clarity of code over optimizations. As for game scripting, Lua is most used one.