Personally, I have paradoxical reactions to both and they actually worsen my insomnia. I am having great success with 5-HTP, which actually raises cortisol. Many people with low cortisol have high adrenaline and low serotonin. Supplements like 5-HTP and L-trytophan raise serotonin in the body.
Read this: http://www.usdoctor.com/cortisol.htm