If I am being realistic, probably Berlin, Brussels, or Paris (maybe also Frankfurt). Specifically these cities, not anywhere else in the associated countries

I'm using the following metrics (and possibly some personal bias):

• A highly developed region that is internationally well-connected and has a strong passport... which leaves us with parts of Europe and some Asian countries. I'm personally excluding UK because of Brexit
• OP didn't mention that "culture weren't an issue", so sadly most of Asia/Scandinavia/Central Europe are out due to difficulty for outsiders to integrate... and among the rest, choices are limited to large, diverse cities that are easy to integrate
• A place that is resilient to climate change, so the entirety of the Netherlands is out (or maybe I just hate NL)

The conclusion is that I should really get aggressive at learning French and German now just in case