Which Diet Pop/Soda is closest to the non-diet version?

I'm not the biggest fan of diet pop, but since I'm trying to watch my wasteline lately, wondering what your opinion is on which diet drink is closest to the non-diet version... (i.e. which diet drink is the hardest to notice that it's diet!)

My two favourites would probably be Diet Sprite and Diet Mountain Dew as I find they are pretty close in taste to regular Sprite / Mountain Dew. For me, Diet Coke and Diet Pepsi just don't cut it - not like the non-diet versions...

Any opinions out there?

Shneebs.