The thing is diet soda is great b/c it has just enough caffine in it. I don't drink coffee at all, hate it, always have, and I probably always will.
At least diet doesn't have nutrasweet like it did in the 80s. And as previously stated, anything in moderation is fine. I'll say I used to drink 4-5 diet sodas a day in college, had to stay up to do hw, but now i've cut it down to maybe a can a day if that. In the summer, it's only as a treat occassionally while eating out.
This is a good debate though.