I'm really struggling to think of a case where I'd pick Necrotic Shroud. A 10-foot radius is practically nothing, particularly when centered on the "caster," so it's no good for battlefield control. I guess... if you're in a fight that's right on the edge, and you're surrounded in melee, and trying to improve your odds of staying alive for one more round?
You pick it for the Frightened effect. Overall I think Necrotic is better than Radiant, but niether are anything special to write home about.