Well, the JVM has Clojure and C# has Clojure CLR, but JVM Clojure is much more mature, stable and battle-tested, so I think the obvious answer is the JVM.
Of course, I'm writing this from the perspective that I'm gonna be using Clojure, which is probably different than your situation. And without knowing more about your situation, it is short of impossible to know which one is the "right" choice.
So without knowing more, I'd say go with the ecosystem and language you're the most familiar with.
Unless your goal is to learn something new, then go with the ecosystem and language you know the least about already.