in the US, "soda" (originally "soda pop") is used primarily to refer to soft drinks, as opposed to "club soda" / "seltzer water" / "soda water"

when i did drink it, i really preferred pepsi. (although vanilla coke was interesting) when i drank a lot at home, it was always decaf. have never done "diet" anything, except occasionally food with splenda in it nowadays.