Arnhem and Eindhoven tied on top as their continentality seems pretty similar. Den Helder is definitely the worst of the bunch imo. Two things surprised me if these stats are to be believed: the high precipitation in Arnhem and the very mild record low in Den Helder. On clear and calm nights with snow on the ground and moderately cold altitude temps, it should have gotten colder than that at some point considering its latitude. I take it the weather station is very close to the sea.
And Arnhem? Orographic lift from the Veluwe hills?