I'm more of a Coke fan. Pepsi is too sweet and acidic for my taste. I believe Coke has more caffeine too.
Sugar makes you awake, hyper, off-task, and when the sugar-high goes away, sleepiness. Caffeine lasts makes you awake(longer), on task, and doesn't make you sleepy hours after. Caffeine pwnz sugar(even though they're both high in sugar XD)
Enough with technicalities, I just think it tastes better XD