Who believes that Robert Plant

Nice try! Hey he's good and all that but not "best," whatever the heck that is.

As evidenced by so many good answers, no on is best. I'd liked to mention a couple of guys with wide range: Arthur Brown and Captain Beefheart.

One would think 'total bs', one would think of another artist or few and I would think my own way as well!
I value Robert not only as big part of Led Zeppelin

Lindisfarne-Great post but you forgot Marty Balin. IMO the best singer of rock ballads from his era.

I saw Led Zep in 1972 at the Balto. Civic Ctr. and they opened with "Immigrant Song". Plant absolutely *nailed* the opening wail, and that is no small feat of you know the song.

I would also have to say that the Who's Roger Daltrey and Free/Bad Co. singer Paul Rodgers were among the best rock singers of all time. Ian Gillian of Deep Purple fame would also have to be in the mix...

As for absolute vocal mastery, I don't think anyone has bested Judas Priest's Rob Halford when it comes to range, power, etc. Listen to their breakout album "Sad Wings of Destiny" to hear a singer that has it all...

-RW-