hammet vs. hetfield is impossible because they are not comparable. it's like math, unlike terms. it just doesn't add up. it's like trying to play Magic against someone with a 52-card playing deck. (not a great analogy).
it's hetfield who makes the Metallica crunch, not hammett. even though hammett is just as good but different.
but about the rhythm vs. lead thing. i believe that the true measure of a great guitarist is to be able to do both and seamlessly go between both of them. Randy Rhoads is the perfect example, he could do both brilliantly and his solos flow smoothly in and out of his riffs. Zakk Wylde can do both as well.
but having two guitarists doesn't mean they can only play lead or rhythm. ah well, i hope i made my point.
thanks for the info anyway.