Great topic!
I must choose, without a doubt, Chupacabras from Lords of Shadows as the most ugly Castlevania character.
Then again, Lords of Shadows is the game with the most ugly characters in general, because it intended to be that way I think. They tried to make the monsters like what they are, monsters. I prefer them pretty, but it's a legit aproach.
About the characters you named, I find Baba Yaga ugly, Merchant and Renon kind of creepy.
Vincent Dorin seems like a nice guy. Brauner is, as you said, an elegant villain.
And Charles Vincent is a handsome old man... in some strange way. He's got class.