Hmmm... I think I'll have to go with coke XP *dodges tomatoes and empty Pepsi bottles*
To be perfectly honest, I like both, and since I'm far too cheap to buy coke OR pepsi, I go with Waitrose own brand coke XP Tastes just fine, and the only reason I've said Coke is because I am addicted to Dr Pepper, so Coke gets my vote.