Cupy was first but at this point you're better of using JAX.
Has a much larger community, a big push from Google Research, and unlike PFN's Chainer (of which CuPy is the computational base), is not semi-abandoned.
Kind of sad to see CuPy/Chainer eco-system die: not only did they pioneer the PyTorch programming model, but also stuck to Numpy API like JAX does (though the AD is layered on top in Chainer IIRC).