Didn't know anyone actually prefered Pepsi!
Coke all the way, any day: Perfect level of sweetness (Pepsi is just a tad too sweet), lovely citric tartness (too subtle in Pepsi) and then you get the exquisite trademark pungent aftertaste.
The only Pepsi that was in any way good was Pepsi raw which isn't really a cola drink in the sense that its flavouring was strongly derived from kola (think gummy cola bottle sweets flavour).