Fra. Definitely connect in Europe and not USA. I hate clearing customs in USA and then going from international to domestic - especially if the international flight was late.

with fra one can really enjoy hanging out near Frankfurt and then using train etc. Granted I used to take train from Nuremberg or dortmund to Frankfurt which was a longer journey…

else enjoy more of muenchen and fly muc-ord. Ah the days when that was flight 906 / 907 before it became ord>sfo!!