I personally do 120-130 degrees, because when I do the scanning for the pieces I extract, the shadows end up naturally on the bottom right side of the pieces. So say I scan a flower, the shadow does get extracted off of it, but the shadows under the layers of petals in the flower itself tend to stay on the bottom and a little off to the right side, so I keep my shadows going that way on my pages so it blends together. I hope that makes sense. lol. Also, when I hold my scrapbooks, I hold them upright so the lighting would come down from the top, placing my shadows to the bottom of the elements anyways

But really it comes down to personal taste.