I`ve met a few great southern Australians... And a few absolutely awful and appalling northern Australians. No awful southerners, and no great northerners.
Have no idea whether that represents a real trend, or just my luck, but...
I also have yet to meet an awful New Zealander so far in Japan, so I am siding that the further south the nicer people.
I was thinking cooler weather correlation, but the absolute most awful and horrible person I have ever met in Japan was from Canada. They may have been a fluke, but who knows.
Best to judge people by their actual behavior.