difficulty is always adjusting. if you refresh whattomine every hour youll get a different number. samething with nicehash profitability calculator. also, whattomine calculates your return at that given moment in time using the following parameters
+150,+500 overclock
65% power limit
nicehash is calculating your returns at stock settings.
no nicehash calculates hash power / hash market price. whattomine calculates est. mint coin / coin market price.