It used to be America, but right now the UK leads the world. The American [record] company was hesitant because 'This Is Love' didn't really work in America.
I think the UK is just kind of a test ground for UK artists before they move onto the US.. it's not that the gp there picks up the good artists first.. it's more that since the artists are from there they put all their effort into getting big there first then move abroad