The Mosh Pit region of March Metal Madness is left with two of the "Big 4," as thrash metal titans Slayer and Megadeth send their most classic albums -- 'Reign in Blood' and 'Rust in Peace' -- into the gauntlet to determine which disc will advance to the semifinals in the battle to determine the greatest metal album of all-time.

In one corner, you've got Slayer's 'Reign in Blood.' The 1986 classic counts anthemic rocker 'Angel of Death' and the explosive live favorite 'Raining Blood,' among its standout cuts. Both songs are key tracks in the history of metal, helping build the band's legacy as one of the genre's greatest acts. To get this far, Slayer advanced over Mastodon's 'Remission' in the first round with 78 percent of the vote, then ousted their fellow "Big 4" brethren Anthrax and their 'Among the Living' album with 71 percent of the tally. But how will they fare against Megadeth?

Well, Megadeth sends their 1990 favorite, 'Rust in Peace' into the ring. Much like Slayer, they have a pair of very recognizable tracks within the history of metal as 'Holy Wars … The Punishment Due' is a live staple and 'Hangar 18' earned them one of their Grammy nominations over the years. Megadeth's 'Rust in Peace' advanced in the Mosh Pit region with greater ease, taking out Testament's 'The Legacy' in the first round with 86 percent of the vote, then besting Slipknot's self-titled release by an 80-20 margin.

So which of these "Big 4" acts will advance to the 2013 March Metal Madness final four? That's up to you. Vote for your favorite between Slayer's 'Reign in Blood' and Megadeth's 'Rust in Peace' in the poll below to help determine the best metal album of all-time.

(This poll will end on Monday, April 1 at 8AM ET. Fans are able to vote once per hour, so keep coming back to make sure your favorite album wins!)

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.