Voice. Most powerful and natural instrument.

I should also clarify that when some can really belt it out that the great ones do it without apparent strain. They don't bend over like they're having a seizure, mouth agape, eyes tightly shut, doing the Joe Cocker thing.
They simply sing way better than the rest of us.

Yeah, In the opera the Barber of Seville the first large group aria, the soprano's voice rises above all the rest (while they are singing full blast) and just shines. Fantastic!!

Friends of my parents were opera singers. She was soprano while he was bass/baritone. I heard her practicing ones in the room and it was unbearably loud. It sounded like regular opera voice 5x louder. I've never heard him singing but when he coughed once next to me it was like an explosion.

In Indian classical music voices sound like instruments almost like imitating them. It is the other way around - instruments imitate perfection of voices.

Handel probably more than any other opera composer I've heard used the voice as an instrument, competing and complementing other instruments in their settings, especially in Julius Caesar.

Nonoise: I could not agree with you more. The current crop of singers all come from the new school of vocal nonsense.The school of vocal hysterics...