Groovy, because it seems to have so much flexibility in what you can do with it. Its' the true "scala" to me in the sense that I can write single line bash scripts with it, but I can also write full fledged complex applications and high performance code that gets close enough to performance with Java and even C++ for most of my use cases. I can switch seamlessly between any level of static / dynamic typing to achieve whatever I want from among these different applications, and I can even do it after the fact.