Used Windows since I was a kid, never had problems with viruses or "security" problems. I have had problems with stability in general, but nothing serious enough to make me want to try something new. That being said it still doesn't get my vote.
Never owned or really tried a Mac. For a home user who runs Windows mainly I see no point. There's nothing the Mac or Mac OS can do that my PC or the Windows OS can't do for me. Albeit it may do it *better* on a microscopic scale, but I've grown with Windows and don't think any gain with a Mac would be worth the extra cash.
Hearing everyone talk about how stable and secure the Mac OS is, is almost laughable. I love how alot of home users do NOTHING to secure their Mac computers because they think the OS is bullet-proof and nothing can hurt them. Talk to any experienced Mac user, you need security on ANY platform or you are at risk. This was just in response to the sackriders...
I'm going to give my Vote to Linux. Because it's free, because it works, and because it's versatile. Gaming has really just become possible for alot of Linux distros (with a little effort), and the compatibility has exploded. Granted you have to find the "version" that fits you best, but when you do it's amazing. Alot of people are just too loazy to give it a try, and don't mind throwing money at M$ or Apple. I for one like free alternatives AS LONG as they work. Ubuntu works for me.