Both are act in their own way.
As Clark: He is a bumbling friendly and really nice guy, He was race on a farm and he is really clumsy, he walk with a arc back he is softspoken. This is an act to distract people from knowing him as superman.
As Kal-el Superman: the opposite of Clark Kent: Broad shoulder, Smile that is like the sun, friendly to a fault, Stood up tall, doesnt wear a mask, when someone look at this guy they doesnt see clark ken they see a MAN a real MAN that is perfect in everyway He is A SUPERMAN!
I believe Clark Kent is the act. Kal-El's true nature is a desire to help people. Even his job at the Daily Planet is -cite issue one, when it was inexplicably called the daily star-not simply a day job to reaffirm his secret identity, but was deliberately chosen to put him in a better position to help people.