To decide whether you want a Mac or a Windows-based PC / laptop, it depends on how accustomed you are to the OS. If you have always been using Windows, I would recommend sticking to Windows because you can have higher productivity with it since you are already familiar with it (no learning curve). If you suddenly switch to Mac, there is a learning curve to get yourself familiar with OS X and you might do stuffs slower than your usual speed for the first few weeks. With that said, you can’t be sure whether you will do work faster on a Mac than a Windows-based PC even when you have finally familiarized yourself with it.
I have always been using Windows because I find it more suitable for me. I can never get used to working without ‘Home’, ‘End’, and actual ‘Delete’ button on a Mac laptop (although there is shortcut key for ‘Home’, ‘End’ etc, but I prefer a single tap of a physical key). After all, you will still work with the same software for your work on both PC / Mac, so there is not much of difference in terms of productivity. The only difference will only be price and personal preference.