Deep Purple was good with Rod Evans. Ian Gillan made them better and Ozzy Osbourne was outstanding in the early days with Tony, Geezer and Ed in Black Sabbath and also later with Randy during his solo career.
I can't vote this.
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And by the way, you can make an allegiance for Greg Lake, ex-King Crimson, ex-Emerson Lake and Palmer.
But Steve Marriott tops all three.
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There is no comparison.
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He was the lead vocalist in the Small Faces and also in Humble Pie.