In general, I think both are important and necessary for overall health improvement.
However, surprisingly, if you were just looking at and either/or scenario and could only choose one, I would say cutting calories and diet would help you to lose weight better and faster. There have been several articles and studies over the last two years that look at this issue. Here is one from the Mayo Clinic: http://www.mayoclinic.com/health/weight-loss/AN01619
I help women and moms be fit and healthy through exercise and eating real food without spending hours in the kitchen or gym.