I like to use mapy.cz when looking at czech republic, because they're veeery recent. Only problem I have with them, is that they are intentionally uncompatible with leaflet. They have their own api/map library and for some reason prohibit usage with other map libraries, because (as per their docs, api.mapy.cz) they believe that accessing their maps directlly is some kind of abuse? Other than that, it's a good product.