I've tried lots of root beers, and so far my favorite is Henry Weinhardt's (yes, the beer co.). So far nothing else even comes close.
But my favorite non-alcoholic drink has to be black coffee. A couple of closer runner ups are a good cappuccino (read: not the starbucks kind), and good black tea with a splash of milk. I have a favorite black tea, but I don't know what it's called cuz i just inherited a box of it from my parents and the label is in some foreign language that I can't read. When it's gone I won't be able to get anymore :-/