I watched an Alton Brown show this morning about how to make Pad Thai. He used what he called "rice stick noodles". I've not made it, but when I've eaten it, the noodles have always been broader and thicker - more like fettucine, for example - can't remember the name of them right now.
Is one more traditional/authentic than the other? He said on the show that the dish was "invented" by the Thai government during WWII as a cheap recipe.