More and more people are openning with 9-13. I don't mind defending it but I would never choose it in a GAYP game as my first. The only disadvantage to the 11-15 is that the opponent can force you into a single corner game which temporarily takes control away but with practice you can get the move back fairly quickly. When confronted with 9-13 the reply I like best is 24-19 although 22-18 is more "book." I never used to believe that a game can be lost after 3 moves but experience has made me face that reality so the opening is super important. The Duckworth Tease is not all it's quacked up to be. :o)