I mostly drink lemonade, and if possible either make my own, or get Turkey hill and cut it about half and half with water; it's like buying lemonade syrup. I -should- drink water, but I find I barely drink at all if I try that, and end up dehydrated. Of sodas I go for caffeine free coke, used to drink a couple liters of that a day but I've cut way back and just keep a couple cans in the fridge, might drink one every couple days.
Out, I tend to get Sprite if they have coke products, or lemonade if they have Pepsi products. Coke's lemonade is vile, Pepsi's entire soda line is repulsive but their lemonade is decent. Coke itself is good but restaurants rarely have caffeine free and if I have any caffeine after 2pm or so I won't sleep that night, good if I'm on a long road trip, bad if I want to work in the morning.