I love the look of wood casing, but I think white is much more versatile. And it would be cheaper.
I worry that I will love it for a year then want white but I cannot put my finger on why I feel this way...I really do prefer the contrast of the white and dark.
I prefer white windows with everything except a white house. If the house was really light I would use darker trim and shutters to help the windows stand out and break up the lighter colors.