Its confusing as to which implementation of Python is appropriate for certain use case or all are just competing with each other ?

Someone from python community should write a blogpost about features, merits and limitations of CPython, PyPy, Cinder, GraalVM and Pyston

To a first approximation, everybody uses CPython, the reference interpreter. Of the other implementations, only PyPy is really production-ready.

I think GraalVM is production ready too, but the JVM is not very popular with the python crowd and vice versa.

GraalPython describes itself as “an early-stage experimental implementation of Python”.