The kick serve is the best serve. Topspin serve which produces a safe and reliable serve over and over again.
it will kick into the opponent. Not many recreational players take time to learn the kick serve but it is the safest. People who hate double faulting should learn the serve. It is super hard to learn at first but will feel natural over time. Some pros have clearly mastered it such as Pat Rafter, Rafter only used a heavy kick serve to serve and volley his way to greatness.
Sam Stosur clearly hits kick serves and when she plays well, then her serve is devastating.
You can tell the serve is being hit because of the path of the ball and where it will jump to. Also you can see the serve based on the upward swing of the racquet.
Madison Keys also is hitting a powerful kick serve.
-DJ ROBO BISCUIT