In "The Problem of Pain", page 27, Lewis mentions, but does not go into the question of whether it was better for God to have created or not to have created. From a Christian perspective, I believe it depends on your salvific paradigm. If you believe in universalism (that all are saved), then humankind must not worry, "For our light and momentary troubles are achieving for us an eternal glory that far outweights them all," (2 Corinthians 4:17) then it was better for God to have created. If you believe that most people end up going to Hell, taking passages such as, "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter into it. But small is the gate and narrow the road that leads to life, and only a few find it" (Mt. 6:13-14), then it would have been better for humankind never to have existed, just as for Judas, "It would be better for him if he had not been born," (Mt. 26:25), since the scriptures speak of him as a man doomed to destruction.