I quite like the B/W female design, because she's more mature than the standard designs. It's nice to play as someone who isn't supposed to be ten years of age for a change...or at least, I don't think she's supposed to be. It's always so hard to tell how old Japanese characters are supposed to be unless you have their age staring you in the face, and even then it's difficult to believe sometimes. But in creating her, I think the developers were trying to create a character that appeals to a more mature audience (this is reflected in the B/W male as well, but not quite as much) and they did a good job with it.
The B2/W2 female is a more traditional approach I think - she looks a lot younger - but her character design is fantastic; she looks like a brunette version of Usagi Tsukino with Princess Leia sized hair buns; I like her for that alone. Her colour scheme is truly awful, but that hairstyle just makes me cackle with delight every time I see it; when I get B2, I will almost certainly be playing as her and calling her either "Serena" or "Usagi" and I'll be modelling my team off of the Inner Sailor Scouts. She's such a wonderfully nostalgic design, so I'd actually be inclined to say of the two, I prefer her.