Which German B2 Language Exam?

I know that in order to apply for Approbation in Germany, you need a B2 language certificate, but I don't understand which certificates are accepted. I'm sure that telc and Goethe are ok, but what about DaF or ÖSD? Or any other? Which exam do you think is easier (shorter, less writing)? I want to take the language exam in Germany because the exam dates in my country don't suit me, but I am afraid that the speaking part would be harder in Germany. Would you advise me to take the exam in Germany?