The Best Metal Split of All Time?

I have been thinking about this question over the last couple of days.  I have several splits in my collection, but really, only one comes to mind as a particular favorite.

March to the Black Holocaust, the split between Vlad Tepes and Belkètre is a landmark release.  It is easily one of the best releases from the French black metal scene known as LLN.  Both groups are at the absolute top of their game.  Each side very well could be a full-length release on its own, but instead the bands have collected them together.  It is a legendary split album, and probably one of the best-known ones in all of metal.

As for honorable mentions, a few have come to mind.  I love the Horna/Behexen split featuring two titans of the Finnish black metal scene coming together.  But Behexen's side is a little lacking on production, knocking the release down a few pegs.  I have a number of splits with Fetid Zombie on them, but they are typically much shorter and the non-Fetid Zombie bands are not always quite up to par.  The better ones have been the ones with Swamp, Hellripper and Battleroar.

There are a few splits that I would like to check out that have the kind of notoriety that March to the Black Holocaust enjoys.  Emperor/Hordanes Land by Emperor and Enslaved respectively is one such release.  It too is a landmark in the world of split metal albums featuring two pioneering Norwegian black metal bands just prior to the scene exploding.  And I hear a lot of great things about the Xasthur/Leviathan split from 2004.  Neither of those bands have made a lot of impact on me yet, but given my recent predilection for black metal recently.  Maybe it is time to check that one out.