Now that´s a difficult question!
RG´02: Serena vs Jen.
Wimbledon: Serena vs Venus
U.S. open ´02: Venus vs Momo.
Oz open´03: Serena vs Kim/ Serena vs Venus/ Justine vs Lindsay.
RG´03. Serena vs Justine, although the hand thingies made it a bit controversial, but it was a good match.
Wimbledon´03: Serena vs Jen/ Serena vs Venus, if Venus was healthier.
U.S. open´03: Justine vs Jen....because none of the other matches were great.