I don't think one group is superior to others, but I guess in my time on earth, I'd say the more pleasant group of people I've dealt with personally are those aged 20-35. I think by this point in our lives, we're coming to find ourselves more (it never really stops, but I think this is one of the more pinnacle points) and figure out our beliefs and come to be more accepting and tolerant of differences. That and some people in this age group are more uncaring about what others do. Not uncaring like they hate everyone, uncaring as in like..."I don't care if you like x or y" kind of deal.
But generally, I don't think you can pinpoint an age group that's nicer or meaner than the other. That's just my own personal observation and I don't speak for everyone in the world, haha. People young and old can change for better or for worse, so that's important to keep in mind. :)