I would reccomend going to UA and LH, if only for the ORD-MUC flight. If you travel to MUC more than twice a year, you're going to be a Premier and have Y+ access if you're in Y. You also have the possibility, if you can get a SWU, of trying to use it on LH (if their ORD-MUC has their new C). I wouldn't stay with AA since they don't have a nonstop whereas UA, the perfectly acceptable alternative, does. Some people might be willing to spend a few more hours in transit to get miles and better status with their preferred carriers, but I definitely wouldn't (as long as there's an acceptable alternative).