Dean gets more screen time by virtue of the fact that he is Clark and Superman, right? So because of the dual roles, my feeling is that Dean gets more screen time than Teri.
However, if the question is "Who gets more screen time, Lois or Clark?", then I would probably go with...hmm, that's a tough one to nail without doing loads of research. I think it's probably a close call, and that it changes depending on the episode/season. Some episodes were Superman heavy, which would make me mad because I was a Clark fan, and Superman was just an interruption, for me.
Between Lois and Clark, I would guess that Clark got the most screen time, then Lois, then Superman. But that's just my immediate reaction.
