As for the question, it really depends. I love all three sodas. I try hard not to keep them in the house because I'd literally be drinking 4 bottles of that shit a day.
Dr. Pepper tastes like shit in a glass bottle and a plastic bottle for some reason, though. Dr. Pepper tastes best from the tap or from a can. Pepsi and Coke taste great in any form. Pepsi doesn't taste all that great from a tap while Coke is fucking king from the tap. As I said, depends on how I'm feeling.
They can all taste like shit if you get them from a shitty tap where they don't refill the syrup or whatever.