If I had to make a list of the top 10:
1. Rob Halford
2. David Draiman(I prefer Dave of course though)
3. Bruce Dickinson
4. Tom Araya
5. Randy Blythe
6. Dave Mustaine
7. Layne Staley
8. James Hetfield
9. Serj Tankian
10. Jonathan Davis
Rob Halford- Come on people, this dude's been around forever! He was excellent in the 1986 videos and is still pretty damn good today. The only problems with him; after he got old, he can barely stand up on stage anymore and can't reach the really high notes he used to be able to without shoving a cheese grader down his throat.
David Draiman- Need I say more? Really fucking aggressive on stage.... and when he's not, he maintains some cool, calm, badass aura around him.
Bruce Dickinson- Pretty bad in studio, imo. Fucking amazing live. Really entertaining and really inspirational. I love him, if not solely, for his respect and dedication to the fans. I dunno, he just seems kinda like a friend XD
Tom Araya- Not the best of live vocalists but somehow manages to pull it off. Really entertaining and one of the best fucking headbangers EVER, imo.
Randy Blythe- Really good voice live and really entertaining.
Dave Mustaine- Pretty damn good live but he doesn't seem to know what to do for the crowd half the time. He's got a good voice and is an exceptional guitarist. But from what I've seen during live performances, it's almost always; "Ok, ummm.... the next song is *insert song with cool voice*"
Layne Staley- A live performance of Man in the Box was all I needed to see.
James Hetfield- Something about this guy just really rubs me the wrong way. Good vocalist and guitarist, but his ego.... Dave Mustaine's ego may be worse by a mile but it's a different kind of ego. In Dave, I see a fucking badass who went through alot of shit in life and is all about self-preservation through hard, life-taught lessons. James is just.... cocky(same reason I'm biased against Kerry King).
Serj Tankian- Good on stage. As strange as his voice is, I sorta figure it'd be hard to imitate some of their songs live, but he manages to pull it off. Plus, he's Serj Tankian. He's someone that you admire, but for the fucking life of you, can't take seriously.
Jonathan Davis- I dunno why he gets all the hate. He's a good and entertaining frontman and like Serj, is able to maintain that unique voice even on stage. The rest of his band is where it all fucks up. The instrumentals are just.... off(live); but Davis is amazing.