I thought Pepsi used high fructose corn syrup. Did you drink Pepsi Throwback?
Regular pepsi uses both HFC and Sugar, and both Phosphoric and Citric Acid, as well as having a higher cafine content, making it a sharper, sweeter, stronger drink than Coke. The higher acid content also makes it more fizzy when it is exposed to oxygen since the sugars pop out more.
Coke uses a higher carbonation level, making it more bubbly, but less fizzy than Pepsi, giving it more of a syrupy, thick texture.
Vanilla coke is a bit better than regular since it has the vanillin to add sweetness, but Pepsi is just, like, it tingles on my throat even after I finish taking a drink and has that strong, smooth citric flavor.
To clarify, Coke uses only HFC and Phosphoric Acid, giving it a much more artificial flavor. I'm pretty sure it use to use sugar and citric acid exclusively, which was probably amazing, but now it just tastes like chemicals.
RC Cola is pretty alright, it just doesn't have a strong enough aftertaste.