Windows, because I've never had any problems with my Windows laptop (it's nearly three years old now). I used to have a Linux laptop that sucked. It made it very difficult to update software and download items because I never knew where anything went. All that I liked were the games on it. As for Macs, I've never personally owned one, but my mom's Mac laptop keeps having freak problems and she's had the motherboard replaced several times, and every other part in it replaced at least once, and her laptop is newer than mine. Plus it was more than twice the price of mine, and has even more cost in repairs.
Voted Windows because I'm using a Windows laptop at home. But I could vote both Windows and Mac, because if you mean which one I use, I use both of them. Windows at home and Mac almost everyday at school. If you mean which one I prefer, I'd probably pick Windows for most things, like for gaming or simply using the internet, in some ways I like Windows better for drawing. I'd pick Mac for things like video editing, animating, working in Adobe programs etc.