In Jorge Cervantez's video "The Ultimate Grow", he suggests for vegetative growth 60-65%. For flowering 50% at the most. Anymore than 50%, fungus and mold start to be an issue.
I agree with everyone else above 60% for veg and 45 or below for flower...i would like to keep it at 30 but my dehumidifier creates to much heat to keep it running constantly so im sitting at 40-50.