Anywhere really. Seems like I do most of my work on the go, though. So I'm a huge fan of writing apps for Iphone/Ipad and Google Docs/Dropbox. Lately it seems like I do the bulk of my writing while at work. (Don't tell my boss! haha) Which again, is made possible only by the amazing portability of cloud files.
I tend to write whenever the inspiration strikes, and if I don't catch it when it's hot, then I have a much harder time trying to remember where I was going with stuff. So waiting until I can find some quiet corner where I can write uninterrupted is a luxury I usually don't have. In a perfect world, I'd be paid to do nothing but write, and could spend every day posted up in my home office with a cup of coffee and no outside interference. But for now, that's just a pretty dream.
I go down to the local library and set up in a private desk. However, this is an urban library, so it's just another hang out spot for kids with free interwebs and games and all, so it's not as quiet as it could be . . . but that's what headphones are for.
As well, I tend to go down to the park sometimes, but it's not as ideal since the sun glare on my laptop screen is an issue.
All I know for certain is writing while I'm home just doesn't work for me.
I enjoy any calm and quiet place. Mainly nature when I can go out and be in it.