It actually depends on the scenario and lighting position. And personal taste.
If you like and have the chance to shoot with some light, and if they wear white umbrellas, you can get a nice luminous image. A bit of glow, but thats part of the magic in the scene.
If they have black umbrellas, they can contrast better with the sky; unless the sky is dark too.
There's a few variables here, and some you can't control like the weather specifics.
Both have the ability to provide great photos in the end.