Not sure about the worse but I think Kim must have one of the "prettiest" voices. I like hearing her speak.
Sharapova's voice sounds a bit strained to me, almost like she is doing like a ventriloquist and not opening her teeth when she speaks.
Venus' voice sounds a bit too young for her.........in my opinion.......but honestly I dont undersatnd the person who says high pitched. In fact I think her (and Serena's) voices sound too laid back and calm sometimes.....not really reflecting what they may be saying in words.