Good to see Anthrax and C.O.C getting mentions earlier in the thread, both excellent bands.
I liked Anthrax with Belladonna but John Bush improved them tenfold IMO, still get shivers down my spine when I hear Only from Sound Of White Noise, I recall James Hetfield at the time describing it as the perfect metal song.
I saw them when they toured We've Come For You All and it was an amazing experience, so damn tight and dynamic, probably my fave gig ever.
For me Bush is up there with John Garcia and Mike Patton as fave singers.
C.O.C have reinvented themselves a few times, not so keen on their early hardcore stuff but Deliverance and Wiseblood are classics.
As for my favourite metal band ever, I'd have to go for Fu Manchu for sheer consistency, Kyuss aren't a kick in the arse away in second place.