If I just feel the urge that I "must" have a soda, then I've found it's best to just drink the regular, sugar-loaded variety. I find that I actually drink fewer sodas that way and my cravings for them get less and less frequent. I actually can't remember the last time I drank a soda (I might have had one last Sunday when I went to the movies), but I used to drink 2-3 20-ounce bottles per day. So, switching from diet to regular soda has actually helped me cut back significantly.
Like Mike said, you can exercise away fat, but you can't exercise away cancer or neurological disorders.
So, I'd rather take my chances with the sugar.