In Germany you need an insurance, but you can choose which one. In Berlin at least I remember TK was the default, but you can choose others.

For clarification, “default” above doesn’t mean “In Berlin you get insured with TK by default”, and rather “Most people in Berlin will recommend choosing TK over a different state-mandated insurer”. TK was also very popular when I was back in university in Frankfurt. It might just still be the one with reasonable prices!