What is the best site to stream popular German stuff (like a German Primewire or something similar)?

I don't know Primewire, so I'm just leaving you the websites of the German public broadcasters here, they rarely have mainstream popular stuff, but maybe something fits your need:

• https://www.zdf.de/
• https://www.ardmediathek.de/
• https://www.arte.tv/en/

If you want to download or watch those productions on mobile, I can recommend https://f-droid.org/en/packages/de.christinecoenen.code.zapp