In my room at home or at the faithful coffeeshop. There's a Panera down the street from the gym, and often after I work out I'll go there and camp, drinking coffee and writing for hours. There's something about being there--no chores or home obligations for distractions, the background buzz of conversation, people-watching for a few minutes now and then--that's very conducive to the writing process for me, whether longhand first drafts or editing on my laptop.
(I do buy coffee and pastry, and I leave if I see the place getting busy so that I won't steal a table with my squatting.)
--Q