Clark knows that he is lucky. If any reporter other than Lois had caught wind of his story, then it would be splashed across the headlines of multiple tabloids, regardless of his personal feelings on the matter.
But Lois keeps quiet, keeps her mouth shut, no matter how famous such a story could make her, being the first to publish an accurate story of the truth about alien life on Planet Earth.
He likes her for keeping quiet.
And then he starts to like her for other things - her personality, her temper, her comebacks, her looks.
But he likes her discreteness the most.