Well, I love Venus but not Serena, and Anna but not Martina

but then it's probably just me being wilfully perverse.
Seriously, I love Venus just because she has so much charisma and personality. Her interviews and press conferences are always fun to read (which is a rarity, to put it mildly), she always looks stunning - in every sense of the word - on court, and since she became a champion she's been unbelievably mature and respectful, always with something nice to say about her opponent. Especially when her opponent's an up and coming player - Lenka Dlhopolcova at the US Open, Daniela at Oz. And before she was a champion, she was totally arrogant - which is, imo, just as attractive. But she's always herself. And she's one of the few people who are physically compelling, who just look amazing, but not through sex appeal - she transcends it.
I love Anna mainly because of sex appeal though

- hey, I like Marat for the same reason so it must be OK. And frankly I don't care about Anna's attitude. I do love her game as well though - she has wonderful finesse when she's on.
Serena - I'm ambivalent about. Her muscles scare me slightly, she's not as gracious as Venus but has none of the arrogant self-confidence Venus used to have, and she misuses the word 'hypochondriac' badly. Don't dislike her at all.
Martina - well, I've never been a fan, but I was pulling for her in the Oz final and after that, I'll probably support her a lot more. The game needs her, she's good to watch, and it's horrible to see someone suffering liek she did.