Train Paris to Murren to Munich

Use the German Rail (Bahn) website to find schedules for trips from Mürren to Munich. (Note, correct spelling, particularly of Muerren {for Mürren} will help.) If you are talking about this Oktoberfest, you might find that the lowest discounted fares are already sold out. I have traveled around Bavaria at the end of Oktoberfest, and did not find the trains to be unusually crowded. Well, there was a somewhat crowded regional train coming up from the Ammersee to Munich on the last Saturday night of Oktober fest, which had a lot of Germans in Trachten, but there were still places to sit. Discount tickets on the Bahn website have to include at least one leg on a train of the Bahn (ICE/IC/EC),and that will probably be the train into Munich, so reserve seats on that train online just to be sure of having a place.

Generally the train will be fastest and likely cheapest - but you ask for best. Best will depend on your particular circumstances. There is no one-size-fits-all travel. How many in your party? Do you want to see things along the way or is time critical? More information yields the best answers.