All of them have shortcomings when one wants multi-threading. Javascript , Python and Lua implementations are single threaded. Perl is slow. LISP is ideal but the commercial distributions with these features have licesing costs of thousand $. The open source (Common Lisp) implementations have all other deficiencies: not easily embeddable and/or big image sizes and/or slow and/or with poor GC. Currently the best open source option seems to be Gambit Scheme. I am playing with it and while the author is extremely supportive some points are still a little bit rough. In the single thread world there is already a clear winner and that is Lua.