You know for such a pop culture aware show, this has always stumped me. None of the Scoobies knew what it meant. Do the 'Alien' movies not exist in the Buffyverse? Because that's how I knew what it meant.
Love Tara, but going with Faith. We've seen Faith fight (and we've seen that she KICKS ASS). We've never seen Tara in a combat situation except that one time she stuck an axe in a demon's back and only because he wasn't looking. As for magic, she sometimes uses defensive magic (like that time she made mist come out of her hands to make a demon blind? I'm not imagining that am I?) but never really used it to combat a demon.