I've never been to the south, so I can't make a comparison, but based on my experiences with the north (moving to York in a few months), I have to agree that the people up north are extremely friendly. From what I have read about southern rents, housing is much, much cheaper in the north. Also, from what I have researched about jobs, the south, particularly London, seems to have more old, established big companies (which would explain the larger salaries), while the north seems to have a lot of small companies, just starting out, lots of IT. Kind of like New York vs. Seattle.
I also agree with what Lola said about the cost of living being much less in the north. I'm amazed at the numbers people mention around here when talking about living around London. My fiance's salary is miniscule compared to some salaries people mention as not enough to live on in the south, and yet my fiance is able to live comfortably up north.