I just started high school tennis practice this week, and I'm not sure if I should buy a new racket. My coach lent me a Prince O3 Tour, and it has been working very well. I've got a lot of money saved up though, if I want to buy my own racket. What are some good 3.0-3.5 NTRP rating rackets? What do stiffness, swing weight, and power level all mean?