About trains in Germany, it is generally pretty good if you are only taking regional trains. The high-speed trains, however, can be pretty bad. I mostly travel regional, and there were no delays the last 20 times or so. I have tried some train companies and the one I liked the most was
db auskunft. Trains in Munich were also fine when I was there. On the other hand, the beer was a new level of strength. To be honest, in your situation, I would choose the train instead of renting a car.