Weekend Rock Question: What Is the Greatest Heavy Metal Album of All Time?

It's difficult to define the term "heavy metal." Where does hard rock end and metal begin? No sane person disputes that Black Sabbath and Iron Maiden are metal bands, but what about Led Zeppelin? How do prog bands like Rush fit into the equation? Can a formerly metal band lose their metal status if they soften their sound? We aren't going to attempt to answer these questions. We're going to leave it entirely up to you.

So what is your favorite metal album of all time? Please just vote for a single record. We know people get very fired up on this topic and some will want to stuff the ballot box with their pick, but please avoid that temptation. If we get 12,000 votes for Megadeth's The System Has Failed, then our system will have failed. 

You can vote here in the comments, on facebook.com/rollingstone or on Twitter using the #weekend rock hashtag.