I guess of the ones listed on the poll I would choose Frank Welker.
Seth McFarlane, can do a lot voices too, I still can't believe he's the voice of Stewie, Peter, Bryan, Quagmire, and so many others on that show, but really those four sound nothing alike at all.
I don't think I would call Tom Kenny a "man of a thousand voices", while he does do a few different voices I can always tell that its him, I just don't think his range is really that big.
I love Jim Cummings, the man can do a lot of different voices. Tigger, Pooh, Darkwing, and Pete sound nothing alike. But he also has a few where you can usually tell thats its him.
But then again I can usually tell which voice actor is doing that voice just by listening to the voice and how they speak. I kinda have an ear for it I guess.