That is a tough one to call. A single "universal" source of light would be the simplest approach and even if the contrast between light and shadow is high, wouldn't confuse the eyes very much. Using the strongest most local source for each structure/artifact might give each a little more individual character, but to much contrast between light and shadow might start confusing the eyes, kind of like having two different sources of light for a terrain map casting shadows in different directions. Like I said, tough one to call. Maybe best to try a test in both approaches and see which looks better.