Mitchondrial Molec. Phylog. - which gene?

[Mark Siddall]

I'm about to start on a project investigating the molecular phylogeny
of 2 different groups.  One is leeches, the other is a wierd group
of protists.
I have worked with the nuclear 16S-like rDNA gene, have primers etc etc.
But for robustness I want to also investigate these from the
mitochondrial perspective.  
The question is which mitochondrial gene to use?  COX-I? Cyt-B? What?
Any suggestions?

Mark

-- 
Mark E. Siddall                "I don't mind a parasite...
mes at vims.edu                    I object to a cut-rate one" 
Virginia Inst. Marine Sci.                     - Rick
Gloucester Point, VA, 23062