… according to Wikipedia, body symmetry

Other qualities tend to rely on frequency of interaction and are not instant

I’d pick Berlin too. Frankfurt was mostly an afterthought and the only advantage it has for me is that it is interconnected so…

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