What is the most impotend hit inthe tennis match??

What is the most impotend hit in the tennis match? Service or Return?

i mean importend, sorry

In Mens tennis, the Serve is the most important, 55-60% of points are won off serve and return, and without a good serve, players wont be able to hold serve, which after one break could result in the loss of the set. In this era of tennis, serve dominates, and without one, high-end players will not make it to the big stage