I'm designing a Billboard in Illustrator. The design on the billboard shows two layers - dropping a thin line of shadow. I've read somewhere, that the shadow looks better if you make it in Photoshop and then put it in Illustrator instead of just making it in Illustrator. But I'm designing a billboard in ratio 1:10 and I'm not sure if the shadow, made in Photoshop, will look good when it's "stretched". Is in this case best, if I make the shadow in Illustrator?
If you are creating in Illustrator, there's no need to implement embedded or linked raster files for a shadow. Use Illustrator.
While Photoshop offers a bit more flexibility in terms of noise and dithering than Illustrator will -- it is highly unlikely, at billboard size, those variances would be of any visual merit.