depends on your preferences...

I use both...

In my opinion, Mac OS is better, I never need to reinstall the OS. I am still using my Macbook pro from 2007, it's never had any problem. it doesn't slowdown without restarting for over a month, (yes, I don't like to restart my computer...)

Windows has its advantages though...for example, Excel under Mac is not nearly as good. it is still better for some apps, especially games. Same game perform faster under Windows with same hardware.