There's lots of discussion on this site already about Offenburg and Furtwangen, and I don't have much to add to that. I had not noticed that the HWR's MBA is now accredited (
http://www.mbaworld.com/MBAWorld/doShowBusinessSchool.action?editbusinessSchoolId=2069) by AMBA.
I think it's very hard to find an MBA-level job in the capital. Berlin is now the administrative capital of Berlin, but it's a very poor city by German standards. For example Berlin has a smaller GDP than Munich, despite having twice the population. There's a lot of unemployment there and there are few vacancies for MBAs. To give some global comparisons, it's poorer than Nova Scotia, Cantabria, Plymouth or Mississippi.
But the position is actually a little worse than that comparison, because the question is really about students in English-language MBAs in Germany. There are very few openings for people without native-level German in Germany (and, as a rule of thumb, English-language MBAs are not take in Germany by people who speak fluent German). MBAs are tightly packed into Hamburg, Munich, Frankfurt and Cologne. They are further concentrated in a small number of MNCs like Siemens, SAP, Deutsche Bank, BASF, Deutsche Telekom, Accenture, McKinsey, IBM, BCG, Hewlett-Packard and adidas.
Of these only McKinsey and Deutsche Bank have a notable cluster of MBAs in Berlin, and they are almost all graduates of world-class MBAs outside Germany (Harvard, Oxbridge, IESE, LBS, Insead etc).
If one must move to Berlin then study at one of these schools, or at least at ESMT (which is a small school sponsored by most of those leading MNCs), WHU, or the Berlin ESCP campus. Indeed, I am sure that if this American colleague wanted to study in Berlin, they would be better off taking an MSc at ESCP than the MBA at HWR.