Depends how you define best I suppose!
I thought Mel was very pretty in BB1, although Nicola had lovely eyes.
In BB2, although she isn't conventionally beautiful, I think Helen was and is stunning.
Narinda is I suspect very attractive in real life, and quite unfairly photographed and represented.
In BB3 - well - difficult. Kate isn't all that pretty, but she's attractive because she's bubbly and enthusiastic. Like Helen she has big blue eyes.
Still, what do I know, I'm a woman, and there are only 4 people I find attractive, all male! 1 of them is one's OH, 2 are one's sons and the other ...........
who could that be I wonder?