I have been to both places and I lived there for long time ( in ooty and munnar ) and in my experience I would like to suggest you that these two places are very different eventhough both are hill stations . Ooty has a Scandinavian looks , the old British churches , bungalows and even the cemeteries of the churches will amaze you and moreover there are lots of places normally the tourist mis like the kodanad view point , avalanche etc etc and you could visit Masinagudi also ( it's around 30 km away from ooty and a wonderful wildlife area where you could spot tigers, elephants, Indian gaur , etc etc ) .In case of munnar its different from Ooty .