There's certainly a bit of bias doing this thread in an Anthrax forum. I'm not as hard on the black album as everyone else is, I thought it was a pretty solid album, and I respected Metallica for making metal mainstream on their own terms (and then they lost all of that respect when they released Load of crap and Reload of crap).
That said, SOWN is probably my second favorite album of all-time behind Volume 8 (although the order periodically reverses itself depending on my mood), and turned me from a casual Anthrax listener to making Anthrax my favorite band. I still listen to SOWN regualrly; I probably haven't listened to the black album in 5 years or so...again, not that its a bad album, there's just other stuff out there I'd rather listen to.
In the end, no question: SOWN wins this one in a landslide