I personally like Trent Reznor and Christopher Hall (Stabbing Westward). I suppose it would be reasonable to argue that either isn't true metal. I just think they are great screamers.
For undeniably metal bands, I'll vote for Burton Bell from Fear Factory.
EDIT: From your poll, I went with Araya. He might not be the best on the list but Slayer kicks so much ass that it doesn't matter.