Racquet Sports Industry magazine provided a list of 19 of the top 20 players' equipment that played at the 2004 Australian Open. Roddick uses a hybrid of Babolat Hurricane 16 and Babolat VS Team 16. Coria uses Luxilon BB Original 16. Of the 19 male pros 10 use a Luxilon BB string, Original or Alu. Four use a hybrid of Luxilon BB and VS gut. Three use VS gut only. One uses Polystar string and as mentioned above Roddick uses the Babolat Hurricane/VS hybrid. The reason I have heard that many of the men use Luxilon is its durability and the fact that they don't want to risk a string breaking during a point.
On the women's side 6 out of 17 top 20 that played at the 2004 Australian Open use gut. Four use Luxilon BB Original/Alu and the remainder use Gosen or Kirschbaum string.