Diet coke gives a cheap sugary taste that is hollow and leaves me feeling cheated. I think it sucks because it uses some artificial sweetener to achieve its zero calorie value. The real original coke has a full bodied feeling that is not wine, but actually has a body to it. Diet also has this weird characteristic of making me hungrier when, I posit, my body feels cheated of calories it expects when it tastes something sweet.
That's just personal impression. You will find this very obvious once you go through two cans of diet (low level torture) vs two cans of original coke.
Pepsi is just a less screwed up version of diet imo. It gives you this sugar rush that is great on the first few sips but quickly becomes bland before the end of the can. This is why it outperformed coke on the sip test, which was actually just a marketing ploy. Pepsi just cannot stand up to coke in quantities larger than a can. It competes with coke because of those first few sugary sips and cheaper price.
As an aside, I loved the vanilla coke. People hated it I think because of the cherry medicine taste to it, but I just did not notice it. When I tried looking for it in a taste, yeah I found what could be described at that. However I think there was a real delicious vanilla taste in it at that complimented that classic creamy taste in coke. Maybe if they found a way to mitigate the weird cherry medicine effect if possible, it would be more popular. Until then, I am a sad panda since no one stocks vanilla coke no more
Root beer has the same body as coke, but is much fuller and creamier and is quite tasty. However this sometimes can be too rich especially if I just had some other greasy or rich milk based food. Coke has a body, but it cuts through grease much better than root beer since its not too creamy.
My favourite drink in a can is, however, not a soda, it's Jasmine Green Tea. Stuff's just awesome. I drink so much tea (not just Green Tea) I speak good English English, talk uppity to strangers and am able to magically sprout a monocle from my eye.