Berlin, hands down. That said many other places aren't particularly 'tech-unfriendly' either. It really depends on what you want to be working on and in which role (consultant, entrepreneur, employee etc.).<p>Berlin is startups all the way but finding consulting/ freelance gigs there can be more difficult than elsewhere and the rates tend to be lower.<p>Rhine-Ruhr mostly is SME, heavy industry and marketing / media (Cologne and Düsseldorf in particular). There are coworking spaces not unlike Betahaus there, too (Unperfekthaus, for example).<p>The dominant industry in Frankfurt is finance (and logistics to some extent due to Deutsche Bahn).<p>Similar aspects apply to the other metropolitan regions.
To bring some context I am a software engineer within the JVM space (Java, Scala) and additional work experience in front end like with libraries like angular and vue