for europe i can say london is the best
For me in the Pacific region, it's Japan. When I was playing on the Tokyo servers back when I was Bronze, everyone there was extremely nice to play with. I somehow never encountered a toxic player—except for the ones playing Yoru, funnily enough. A lot of people there focus more on team play, so clutches happen less often since they rarely make selfish plays and tend to be more reserved.
What really impressed me while playing on those servers was that everyone knew how and when to save. That was something no one did back then, especially on the other servers I played on (Hong Kong and Singapore).