So start with the subject you want to study, or with the kind of city you want to live in. Do you want to live in a big city or a small city? Do you prefer a big university? What's your level - do you need general teaching or do you want to get into specialities? In the first case, any university that offers the course is fine, in the second, look closer.

As far as I know, all universities in Germany are more or less equivalent. In Germany no one will ask what university you went to, when you apply for a job. Unless it's an applied university (Fachhochschuhle).

With that in mind, I would recommend you to choose your mayor first and then figure out which university has English speaking programs for that mayor. In Germany you have to choose your mayor before you apply to University.

if you like seeing your universities in ranking form