You are in a no-sense PC/mac computer battlefield and you are forgetting the more important feature: Cubase/Nuendo are both multiplatform compatible. You use software (master) on hardware (slave)- reverse this relationship is a mistake. I have used cubase/nuendo on mac since 2001 and perhaps my next computer could be a PC
If you know well windows OS go on PC. Do you like mac “pussycat” OS? go on mac (is the choice for a lot of cubase pro users). Moreover, PC/mac can live together: ie. a macmini Cubase master Ethernet wired to a PC VEP-slaved with full samplers libraries onboard… I think yo must be guided for OS knowledge and budget in your choice