There is, as expected, a balance between both the exercise completed and the calories taken in, and one's weight. It is nice to see that over the years, women who exercise regularly every day (apx 1hr of light workout) were able to roughly maintain their weight.
So, to answer whether it is more important to diet or exercise: both!
It seems like it may be easier to lose weight by controlling ones diet, and better to maintain weight by consistent exercise. So, neither is a golden ticket, but together they work pretty well. :)