depending what you mean by worst and best attitude.
As for having the worst attitude, I would definately say Lindsay. She gets so down on herself, and in big matches, if she misses on deuce, or 30-30 at an important point, she loses the game and the match because of herself, as she just slumps her shoulders and gets down on herself. I just knew it was going to happen at the start of the third set against Venus, this past Wimbledon.
The most unsportsmanlike, however, has to be Justine.
The best sportsmanlike attitude is either Kim or Venus.
But the best mental attitude (except when recently playing Serena) has to be Venus. Man, her on court demeanor, and her mental strength are awsome. If you dont believe me watch the Miami 2001 final, or the US Open 2000 semi.
I think Jennifer and Serena have brilliant fighting spirits out on court and never ever give in, and their attitudes alone have brought them through many tough matches, just by their greater beliefs in themselves, than their opponents.