I would think to be considered "Best Soundtrack Artist" you would have had to do more than a single successful soundtrack... if it was based on a single soundtrack, I would say Peter Gabriel for the movie "Birdy" or Air for the movie "The Virgin Suicides... But being that it is "Best Soundtrack Artist," I would have to say Graeme Revell. He has done the score to such movies as The Saint, The Craft, The Crow, all of the Sin City movies (the first, and the two that have yet to be released), Strange Days, and a ton of others. I still listen to the first Crow score at least monthly.