Generalizations about the friendliness of entire regional populations are inherently flawed and misleading. Both "Northerners" and "Southerners" encompass incredibly diverse groups of people with a vast spectrum of personalities, cultural backgrounds, and individual experiences.
Friendliness is an individual trait, not a regional mandate. You will find warm, welcoming people and reserved individuals in every corner of the country. Attributing personality characteristics to broad geographic labels oversimplifies complex social dynamics and ignores the rich diversity within any region.