Nuns are the "Brides" of Christ - hand maidens so to speak, and take three vows: poverty, chasity, and obidence. Not all priest societies take all three vows. Nuns can not perform a Mass, one of the most important roles of a priest.A nun's soul is not marked forever with "nunhoodness" once she makes final vows. A priest's soul on the other hand, is marked forever- once a priest always a priest- even if he's defrocked. So he could go to hell in the collar. The question is would a man want to be called a hand maiden?Or godforbid, a bride? I dont think so.
Monks and cloistered nuns, as a rule, are retired from society and forgo community outreach.So I quess their "ranking" is about equal.By the same token, Brothers and non-cloistered nuns do communty and missionay work. But I might give the prestige award to the monks, though. Both Gregor Mendel and Martin Luther were monks, and you know what happened next.Besides, what is New Year without champagne?