IMO, since an artist's greatness is measured by awards that he achieve, id go for mike portnoy...
"Best Up & Coming Talent" (once) "Best Clinician" (two times)
"Best Educational Video/DVD" (two times)
"Best recorded performance" (6 times)!!!
"Best Progressive Rock Drummer" (for 12 consecutive years)!!!
Also the second youngest person (at 37 years of age) to be inducted into the Rock Drummer Hall of Fame since Neil Peart was inducted in 1983 (at 31 years of age)
And has most recently won The Spirit of Prog award from the 2009 Classic Rock awards with his band Dream Theater, where they were also nominated for Album of the Year for their release, Black Clouds and Silver Linings.