Diet versus exercise, what contributes more to pure weight loss?

One should not work properly without the other one. Exercising beyond your body capacity, and without an adequate diet may bring many problems. Also, you won't lose as much weight just with a diet, so you'll need exercises anyway.

Of course I'd continue doing both, I'm just curious as to which one has a higher impact over the other in the long run.

For example, if I exercised twice as much than I do now with a more moderate diet versus exercising as much as I do now but with a stricter diet.
The lack-of-progress thing is annoying me. :\