How could you not chose Serena's GS Titles?
First of all, short of the Grand Slam, for posterity there is nothing more impressive than holding both the French and Wimbledon at the same time. Making the transition from Queen of Clay to Queen of Grass is the ultimate. Is there an active player that can make the same claim (I know Monica, Chucky & most recently Venus have come close)?
Second, the US Open is more impressive than the Aussie (no offense, Aussies). Back when I first started following the pro game (an old Connors fan, I am), it was common for top players to blow off the Aussie. This is part of the reason they moved it to the beginning of the year.
Third, if you are a current player (meaning not retired) the most impressive Grand Slam titles to hold are the most recent Grand Slam titles
I can assure you JCap and Lindsay would rather be the current French and Wimbledon champs than the former ________ champ or the current Aussie Open champ.
Never winning Wimbledon will be a black mark on JCap's resume.
Never winning the French will just be a glitch on Lindsay's
Never winning the Aussie will...
...who are we kidding? Serena's going to win the Aussie next year (If Venus doesn't beat her to it).
Don't get mad Lindsay & JCap fans. The most of the rest of the top players wish they had your fave's titles.