Hi, My son, 12 years old, plays tennis for three years, about 10-12 hours a week. He uses a prince more attack s920 racquet/prince lightning xx16. A friend gave him a Volkl c10 pro 98/prince synthetic duraflex 16 to try it. What is your oppinion about racquet choice and what is the best string for the volkl c10 pro? Thank you very much.