I prefer Afri-Cola.
It's german brand and they've been around for quite some time, but lost a lot of market share to the big ones and because they kept changing the recipe.
A couple of years ago, they listened to their fans and switched back to the original old recipe. Was the right decision, it seems - they had a bit of a comeback during the last years.
Aside from the great taste, I like them because they've got 250mg caffeine per liter.

Don't know if Afri-Cola is sold outside of germany, but if you've got the chance, you should try it.
When it comes to Coke vs. Pepsi, I always preferred coke. Pepsi is just a bit to sweet for my taste.
So during my first trip to the US, I was quite surprised to discover that the Coke there tastest different to the coke produced for the german market: US coke is sweeter, but contains less carbon dioxic gas. I've been trying coke in every country I visited since, trying to compare. Most of the time, it's hard to tell if there are differences, but between german and US coke, its quite significant. Did anyone make the same experience with coke in different countries?