Stephanie Meyer because of her pro-abstinence Mormon propaganda. I've never read Sparks but I don't think his books are explicitly Christian, though they're probably close to it.
There is nothing religious in Sparks books AFAIK. He just avoids very explicit sex scenes to retain a "clean" image so he can sell books to people with traditional moral. Its business, not faith.
I have read one when I tried to familiarize myself with how different formula writers do their stuff, and he is technically very good and has an efficient language. I think it was boring because its so obvious in its methods and "tricks", but he is very good at what he does.