Question
I have a wildflower area in pretty much full sun.  
 What is the best kind of mulch to conserve
moisture but still let the wildflowers seed out?

I live in region 5

Answer
Mother Nature generally provides such mulch as is needed.  Wildflower meadows should be mowed or burned late in the season.  If you mow, that will provide mulch; if you burn, mulch with leaves that do not mat heavily like maple leaves do.  If that is all you have available, run the leaves over with the lawn mower or put them through a chipper first.