There is tons of stuff on Pubmed on the topic of pressors in shock, but the only two articles I found that compared the two drugs head to head clinically in humans were these. I think the pdf's for both of these were available for free:
Comparison of phenylephrine and norepinephrine in the management of dopamine-resistant septic shock. Indian J Crit Care Med. 2010 Jan;14(1):29-34
Phenylephrine versus norepinephrine for initial hemodynamic support of patients with septic shock: a randomized, controlled trial. Crit Care. 2008;12(6)
This article provides a good overview / review of the clinical usage of vasopressors & inotropes in septic shock:
Inotrope & Vasopressor Therapy in Septic Shock
I still haven't really gotten to the guidelines; been busy doing family stuff and studying for a pharm exam that is scheduled on my first day back from break.
Its good reading, always nice to expand the knowledge base just a little and have a better understanding of why