People have started wars over this simple question..
I agonized over that same issue a few months ago when wanting to upgrade my old XP machine.
I wanted to buy an Apple for the perceived ease of use and reliability, but I couldn't justify the cost after having the many cheap PC's I've owned since the beginning of time, and it may or may not run some things I wanted even with their fine emulators.
All I wanted was a fast machine to play a few 'first person shooter' type games, and browse the internet safely.
Unfortunately, the 'good' games are usually Microsoft Vista/Windows 7. And some people think Microsoft is an internet target for bad things.
So, I went to Newegg.com, bought all the parts and built my own box, which is now stupidly easy to do. I loaded Ubuntu on one disk drive for my main email/internet machine, and Windows 7 on another disk for my games and some old XP programs.
So, for a few hundred dollars I put together a mid-high end box ( 8Gb ram, Tri-core 64bit AMD cpu ) that would have cost thousands in an Apple store. A hard decision since I like Apple alot, as in their Iphone and company stock!
That being said...
I ran my Windows/ Microsoft boxes for years, and still do, with no virus problems by using readily available anti-virus programs, some free, some commercial.
When I come to this forum it is on the Linux side using Mozilla Firefox, and it is much faster than the IE8 on the Win 7 side...
For me it was a cost vs function issue..
May not be the black and white answer you are looking for ... sorry