Jun 18, 2015 - 4:41 PM
Hi furmanskil, welcome to MySwissAlps!
If you'll be traveling intensively in both the Bernese Oberland and the Zermatt region, the best choice is probably a rail pass covering the whole of Switzerland, with additional regular tickets to Austria and the Czech Republic. Examples are the Swiss Travel Pass and the Swiss Half Fare Card. It's hard to tell though, since it all depends on specifics. This guide may help you to find the best pass.
If you're still unsure, could you provide us with more details on your itinerary in that case? What will be the exact route you're following? How long do you intend to stay in Interlaken and Zermatt, and what kind of day trips do you plan to make?