First question: do you want the trip done in just one day? If so, it is best to take the fastest train to Zürich then route your trip Zürich - Interlaken - (whatever Berner Oberland village) through Luzern and Brünig (a very scenic route).
The whole trip would then take around 8h, give or take depending on the exact connection, with 4 or 5 changes. Checking prices for next Tuesday, I found tickets as cheap as 35 Euro (all-train, no bus) on www.bahn.com . The German railways can sell through-tickets in almost all Swiss lines now, including the meter-gauge railway between Luzern and Interlaken (the scenic sector), often at ultra-cheap German prices, for trips that start in Germany.
If you have two days, you can then travel via Innsbruck to Zürich, and follow Zürich-Interlaken via Brünig (as above) the following day. You should, in this case, buy tickets on the Austrain railway website (www.oebb.at) for Zürich and scoop a Saver-Day Pass for the other sector (you can combine that with a 4-5h walk around in Luzern).