Ozzy simply because of Zakk Wylde and his great vocals.
Zakk Wylde and Ozzy have no affiliation, you may be confusing Ozzy Osbourne for Black Sabbath, which Ozzy Osbourne is lead singer of. Zakk Wylde, however, is a member of Black Label Society, not Black Sabbath.
I'll go for Ozzy, though I'm not a big fan of his solo career, I love his early work with Sabbath.
Out of those four I like Slipknot the best. The only thing is that it seems like they have a bit many members, I mean most bands only have four or five and they have nine. It sometimes makes me wonder if they would sound like crap with a normal amount, but oh well. Psychosocial and Dead Memories are good songs.
