Not necessarily from a musical standpoint, but individual talent. Also, they have to be living & still making good music. Also, only 1 person per band max (but you can choose someone to play 2 instruments).
Also, I know this should go in Greatest Hits, but it won't let me post there for some reason :-(
Lead Guitar: Angus Young (AC/DC)
Rhythm Guitar: James Hetfield (Metallica)
Bass Guitar: Steve Harris (Iron Maiden)
Vocals: Ronnie James Dio (Black Sabbath/Heaven and Hell)
Drums: Dave Lombardo (Slayer)