We're down to the final four acts in Loudwire's March Metal Madness 2013, with each of the four regions crowning a champion. We're one step closer in naming the greatest metal album of all time, and the competition has been narrowed down to both classic and modern legends.

The godfathers of heavy metal, Black Sabbath, grace the semifinals with their immortal 1970 album, 'Paranoid.' In an all-Ozzy battle in the quarterfinals, 'Paranoid' took out Ozzy Osbourne's 'Blizzard of Ozz.' 'Paranoid' only needs two more wins to take the entire competition, but they've got the most successful metal act in history to slay first.

Metallica have never taken a loss in Loudwire's March Metal Madness history, having won the 2012 tournament with the song 'Master of Puppets.' After taking down Pantera's 'Vulgar Display of Power' in the quarterfinals, Metallica are looking to extend their undefeated streak with their 'Master of Puppets' album. But can they beat Black Sabbath in the semifinals?

Black Sabbath's 'Paranoid' or Metallica's 'Master of Puppets'? Vote for your favorite album in the poll below!

(This poll will end Thursday, April 4 at 9AM ET. Fans are able to vote once per hour, so keep coming back to make sure your favorite album wins!)

Update: Metallica have defeated Black Sabbath and have advanced to the Championship Round. To vote in the final round, click the red button below:

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Spread the word on Loudwire’s March Metal Madness 2013 and earn a chance to win a $100 iTunes gift card. Just follow @loudwire on Twitter and retweet our announcement by clicking the red button below. Entry period ends April 9, 2013. See official rules here.