Guess I'll be the one dissenting vote when it comes to the basement. I'd stay upstairs! Mine is on the second floor, the sunniest of the two bedrooms. Great light during the day. Also, gets me out of that "cave" environment; i.e., I work in an office building all day.
Another reason... we've all been griping about our over-stocked, messy, disorganized sewing rooms. Mine's the same, plus some. What better way to limit yourself and enforce organization than staying in a better defined space? Why not use the basement when it comes to pinning and quilting large tops?
Just my opinion.