Who does not want a killer smash in badminton? In fact, it is not a want, it is a must. After all great smash is needed to finish rallies. To produce a powerful and steep smash, you need swing speed, optimum angle/point of contact and maximum transfer power from racket to shuttle.
Simply speaking, a heavier racket will transfer more power from racket to shuttle. However, a heavier racket will also reduce the swing speed and can make it harder to time the angle and the point of contact perfectly. This is where the balance of the racket comes handy. For the same weight, a head heavy racket will transfer more power to the shuttle however it is a bit harder on the body and the post-shot recovery is a bit slower. The technique is paramount since it drives consistency in shots, efficient use of energy and long-term physical endurance. And, thus for a beginner/intermediate player, the racket characteristics that assist in developing and honing the technique must hold primacy. Thus start with a 3U or 4U racket which feels right for your physique and strength as far as racket weight is concerned and starts with a well-balanced racket and transition to slightly head heavy rackets particularly if you play singles.
In the video below you hear a discussion about the racket characteristics that produce a powerful smash.