One area in which Numba probably wins is that it's aware of Numpy arrays as types for the compiled functions. There's a lot of code that handles with Numpy arrays, and Numba integrates nicely with that.
Newer versions of PyPy also support a subset of numpy.
PyPy does, but I don't think that the RPython translation and compilation layer knows about the numpy semantics, so I don't think that helps RPythonic make extension modules.