Coke. Though I'll drink either. If it comes from a can, Pepsi. If it comes from a bottle, Coke. But as a general policy? Coke.
Well, Pepsi is just like a flatter Coke, really. Aaaaalso, I don't actually drink soda much, but when I do, I prefer Root-beer. ROOT-BEER MASTER RACE ROOT-BEER IS BEST RACE ROOT-BEER/10 PEPSI AND COKE IS 4 SCREBS But out of the two, I like Coke more.
I prefer seltzer, when it comes to carbonated beverages. (That is, I don't drink soda because it has sugar or other nasty sweeteners. In short, you should be eating your calories, not drinking them.)