I heard Cash's cover well before I heard NiN's version...
Then in that case Cash made it classic. Another song I never skip on my iPod.
I'm not a huge fan of Cash's cover. Love the NIN version though.
I do like this quote from Reznor about the cover though.
Reznor said that when Rubin first asked if Cash could cover his song, he was "flattered" but worried that "the idea sounded a bit gimmicky." He became a fan of Cash's version, however, once he saw the music video.
"I pop the video in, and wow… Tears welling, silence, goose-bumps… Wow. I just lost my girlfriend, because that song isn't mine anymore… It really made me think about how powerful music is as a medium and art form. I wrote some words and music in my bedroom as a way of staying sane, about a bleak and desperate place I was in, totally isolated and alone. [Somehow] that winds up reinterpreted by a music legend from a radically different era/genre and still retains sincerity and meaning — different, but every bit as pure."