I drink all colas, or atleast try them out. And I like all the three major names available in India - Coke, Pepsi and Thums Up. Personally I prefer Thums Up, because it is the most fizzy. Have you grown up to Thums Up yet :-)
People say carbonated drinks are bad for your health, and there should be some truth in that. But I feel they are more thirst-satisfying than non-carbonated stuff. And it helps to alleviate problems with acidity and connected gas-troubles. That remains the only reason for my preference for them.
It’s tough to say the Pepsi is better than Coke or otherwise. IMHO, it all depends on the bottling plant where it originated. I have found this very funny, but true. While in the state of Kerala, India, I go for Pepsi, but in Bangalore I prefer Coke as it is more fizzy. While in Europe, I felt that both are different, yet equally good (or bad?).