Not so much a preferred choice but what I already know & use. You will get far more votes for windows & mach3 not because it is better but it's because it's what people have & know. You buy a computer it comes with windows or mac operating system already to go. That is enough for most people & there are still a lot of people who wouldn't have a clue about changing the operating system on a machine & would never touch it.
I run windows because I can get help & support for the software I use easily which you can't always do with other operating systems including mac but then most of the software is for business use so I can't afford to have problems. If I had a driver problem & a printer not working correctly I can call the tech department & get help straight away running windows as they all know & use it.