Which Scandinavian country as the most welcoming/friendly people?

I've lived in Denmark for a year and I've traveled to Norway and Sweden. I found it easiest to make friends in Norway, but maybe that's because I only went to Oslo which is a big city, whereas in Denmark I lived in a small town. So I suggest you go for major cities only. As a tourist you will probably want to stay in a hostel so you can make friends among your roommates and while cooking your food in the kitchen. I also noticed that the Danes are more alike to each other, even the immigrants try to adopt the Danish ways for everything, whereas in Norway you will find a lot more diversity.