From The Historical Present:Demystifying Diet Coke (sorry for reprinting so much of it, but this is too cool to resist):
Diet Coke - Although it came out two years before “New” coke, diet coke that we’ve enjoyed since the 80s is the sugar free form of new coke. In other words, it’s based on the formula for the “New Coke” that wasn’t released yet (it debuted in 1985) when Diet Coke hit the market (1983), and is also now no longer available. (the New coke). Coca Cola has no plans at this time to discontinue the aspartame based Diet Coke, as it is third in the soda market. (After Coke and Pepsi, respectively.)
Diet Coke with Splenda - You can spot it on shelves by the yellow bit in the label and the blue caps - this is a late to market response to those Diet Coke drinkers and Atkins dieters who wanted a Splenda sweetened soda. This is based on the same formula as Diet Coke, but because the sweetener has a different taste, the taste of the drink is closer to the way “new Coke” tasted, or for those too young to remember - a slightly sweeter version of Coke.
C2 - Half diet coke and Half “real” coke - for those who wanted to reduce the amount of sugar but weren’t ready to give up everything just yet. Sweetened with a combination of high fructose corn syrup, aspartame (Equal) and sucralose (Splenda) .
Coca Cola Zero - Sweetened with aspartame and acesulfame potassium., the reason this is different than Diet Coke is Coca Cola Zero is a sugar free version of the Classic Coke formulation. In other words, this is meant to be a sugar free version of the red cans of Coke you know and may or may not love. It has a redder, deeper color close to the color of Classic Coke and tastes far less like a diet soda (by many accounts) than Diet Coke.
Coca Cola Light - The European version of Diet Coke - slight variations from country to country based on food regulations, water quality and fidelity to syrup to water ratio account for taste variations, but this is largely Diet Coke with a different name to conform to local food labelling laws.
Well, I drink only Classic Coke anyway. Now, why is Classic Coke the best in small glass bottles, followed by 1L glass bottles, and the worst in 2L plastic bottles?