Eh, for us its just a matter of labels.
I define them as "Metropolis Clark" (though I often shorthand that to just Clark, and thats my bad) "Smallville Clark" and "Superman."
Smallville Clark is the full person, no secrets, not hiding a part of who he is. Not playing up certain aspects of his personality to fit the expectations of the role he happens to be in. I think most people call this aspect of the character Kal. But Im difficult, so its Clark.
He's the guy who listens to alien music while repairing a tractor (and maybe also building a time machine on the side, and not even really seeing much of a difference in the tasks).
Metropolis Clark is an act; the mild mannered reporter who acts shy and cowers in front of muggers. Yeah, there are parts of the real person in there, but this is the guy who has to hide who he is from his co-workers, and thus its largely a facade built on the foundation of his personality. He's the guy who trips over his own feet, and through the confusion that causes, saves someone from hurting themselves on the other side of the building.
And Superman is the best aspects of who he is with the volume cranked up to eleven, his shortcomings and flaws ignored as much as possible, and fully embracing the fantastical elements of who he is. He's the guy who never shows a break in his confidence and always seems to have the answers and a plan of action, regardless of how worried or shaken he might really be.
The older I get, the more I see a divide between aspects of who Superman is. I fear Im slowly becoming kurosawa (for those who remember him from the boards). If I ever start talking about Superman having a weird case of schizophrenia, stop me for my own good.