To me, with that part subtracted, both versions of the same. Goofy lyrics about the apocalypse weren't any better than lyrics about bangin a chick. To Metallica's credit, they managed to twist the riff and make it give off the feel of galloping horses whereas Mustaine executed the song to that of a whirrng car motor. It speaks volumes to the versatility of the riff, but that middle section is what makes it undebatable that Four Horsemen is the better song.
You know its true, bunny rabbits we have got lovely little fluffy bottoms. We do. That's why people often mistake us for Danny Devito.