Why do you ask at all? If you know java, use it. If you know c (well, not c) - if you know python, use it. If you have to learn something, because you don't know any language, get a job first and think about a startup after you dream in (put here any language).
Any scripting language basing on java will be slower than java. My opinion is: if you can avoid another software layer, avoid it. It makes you depend on more code that you don't control, slows down your apps.