What we are always told:
Diet and exercise are both important. If you do only one, and not the other, you will not succeed.
What I found to be true for me:
Exercise never helped me to lose weight. It was usually either a distraction, or messed with my diet, or even worse, gave me pain and injuries. I've seen some news lately that suggests exercise is important for health, but not actually effective for weight loss.
So, my experience was that changing my diet (i.e. less carb more fat) allowed me to get to 70% of my goal. Now I am able to exercise without hurting myself, so I started a modest workout plan. It has slowed down my weight loss, but I am not too concerned.