You don't really have any choice. The countries which have adopted the Euro do not have a currency of their own - as it was replaced by the Euro, and the countries which still use their own currency do not (officially) accept the Euro. It is however true that the Euro is accepted in some tourist shops in non-Euro countries, but on a limited basis and at exchange rates set by the merchants themselves.
Of the countries you mention, the Netherlands and Germany use the Euro, Denmark uses Danish Krone and Sweden uses Swedish Krona. The Danish and Swedish Krone is not the same currency and you will not be able to use Swedish currency in Denmark or vice versa. By using ATMs in the respective countries, you will always get the country's official currency. This is usually the best way.