We will arrive in Munich early Wednesday and then leave Friday morning for Oberammergau. While in Munich we want to take a day trip to Dachau and maybe one other destination. On Saturday morning we depart Oberammergua for Interlaken Switzerland and want to use Interlaken as our base for daily travel around the area and the entire country as well. Then we travel to Geneva for our trip back to the USA. Our daily routine in Switzerland is to travel by train to many different destinations. We are 60+ in age and and want to travel first class. What type railpass would be best for our trip? Eurail? Two Country pass? Other?
In the first place, a €28 Länder-Ticket for seeing Dachau would be overkill. For €12,30, the same number of people (up to 5) can travel to Dachau, RT, on both the S-Bahn and the bus, with a Munich XXL Partner Tageskarte.
Oberammergau, for more than one person would best be done with a Bayern-Ticket (one form of Länder-Ticket, €28 for two people.
As far as Oberammergau to Interlaken, Steve is right, you can get advance purchase, non-refundable tickets for a low as €39 per person. These tickets are for 2nd class. You have obviously never been to Europe, or you would know that 2nd class is perfectly adequate.
So, for the first three days, you're looking at maybe €65 per person, downtown Munich to Interlaken. You can't beat that with any railpass.