Question
Could you please tell me what the rarest, most beautiful flower is. Thankyou.

Answer
There is no objective answer to this question.  People have different tastes.  In North America, Yellow Ladyslipper Orchid might be considered to be it by many.  If you mean in the entire world, I couldn't possibly know the answer, but there might be an elusive orchid in the Amazonian jungle that would qualify.