though, if you want a good root beer see if you can get a brand called boylan's (think i spelled that right). they actually have a whole line (cola, ginger ale, orange, grape, root beer, birch beer, black cherry, creamy red root beer *drool*) they are all good, but top three is def black cherry, root beer, and creamy red in no particular order (it changes for me depending on mood). if you're in the NJ area you'll have a better chance of finding it as the plant is in NJ and its more of a local brew.
but in a general sense, my fav is root beer
-Darth Simon