I’ve been buying and reading Christian fiction for a long time.
Many of the first books I bought and read had illustrated covers. Most look horribly dated now because of how much illustration styles have changed.
But the photographic covers from the same era also look dated, especially the contemporary titles, because clothing styles have changed.
The rise of imaging software such as PhotoShop has changed the look of photographic covers. It’s now relatively easy to merge multiple photographs into a single cover image, which wasn’t possible back when I first started buying Christian fiction.
Now, the choice between photos or illustrations on covers seems to be largely driven by genre.
Women’s fiction and rom com are more likely to have illustrated covers than, say, historical romance or romantic suspense. Contemporary romance can go either way.
Overall, I can’t say I have a preference. I wouldn’t choose or not choose a book because it had an illustrated cover … or because it had a photographic cover.