When I went into a Salvation Army used store one time, they had a shelf marked fiction. That was the section where they put the bibles. I thought it was very appropriate.
I avoid anything labelled as Christian but I have read good science fiction stories that dealt with Christianity.
One of the most memorable as Arthur C Clarke's short story, "The Star."
And another memorable one had clones of Jesus and Bhudda.
But neither one of these were specifically Christian fiction or science fiction.