Which Europeans have the most Neanderthal DNA?

Probably the Basques. "The Basques have occupied much the same area of northern Spain and southern France for thousands of years, extending further eastward and northwards into Gascony and the Pyrenees, as attested by archaeological and toponymical evidence, and their Basque language is considered a language isolate. It is widely held that most likely the Basques are the last surviving ethno-linguistic group descended from populations of Neolithic Europe before the intrusion of Indo-European languages and peoples."