Let's begin with the fact that these are two completely different applications. One was built to work with Windows and the other one was coded specifically for macOS.
As for today, Babylon for Windows is more advanced and offers more features than Babylon for Mac. Babylon for Windows includes formatted document translation and the Babylon Human voice. While Babylon for Windows supports the Babylon click on any word that appears on your screen, Babylon for Mac currently supports the click in specific applications - however, our developers are hard at work to bring the Babylon click to the same level as with the Windows version.
In terms of the translation quality - both applications provide the same quality of translation.