Singer - Phil Anselmo: Racist stage antics aside, in his prime, his screams were pure power and his cleans were beautiful.
Guitarist - John Petrucci: The perfect blend of melodic and technical. Everything that a lead guitarist should strive to be.
Bassist - Cliff Burton: This one is more personal with me being a bassist myself, and Cliff is the biggest reason why I started playing the instrument. In a genre that usually puts the bass in the background, Cliff made his playing stand out, adding fills and flair to his basslines and taking solos. I know it doesn't get much love on these forums, but the first time I heard (Anesthesia) Pulling Teeth was a revelation. It showed me that in metal, a bass could be used for more than doubling the rhythm guitar and could have it's own identity. Cliff Burton helped shape who I am as a bassist and as a musician today.
Drummer - Mike Portnoy: Nobody makes their hi-hats sing like Portnoy. I could listen to his isolated drum parts and still enjoy them as if they were a full song.
Bonus musician!!!
Keyboard - Jordan Rudess: He's not called the Wizard for nothing. His technique is unmatched, his compositional and orchestration skills are amazing, and his mind for technology is revolutionizing music applications.