Merlin’s del.icio.us page points to this explanation by Leslie on the different make-ups of the different diet sodas now available from Coca-Cola. For the record, I've tried them all, and my own personal taste test results are as follows: Diet Coke - I knew there was a reason I never liked "New Coke," and having a non-sugar version only made that worse
Diet Coke with Splenda - new "New Coke"; better than the original, but still not something I'd pick up
Coke Zero - nice try, and it would be a toss-up between it and the Diet with Splenda
C2 - as close as you can get to the authentic Coke with a diet version; if I can't have, or would rather not have, the Real Thing™, this is what I drink Though I have been rather successful at keeping soda of any kind to a minimum in my diet. Which means if I'm going to have one, I may as well have the original, non-diet version.